diff --git a/mod/assign/classes/completion/custom_completion.php b/mod/assign/classes/completion/custom_completion.php
new file mode 100644
index 0000000000000..4753324f9c1c0
--- /dev/null
+++ b/mod/assign/classes/completion/custom_completion.php
@@ -0,0 +1,82 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+declare(strict_types=1);
+
+namespace mod_assign\completion;
+
+use core_completion\activity_custom_completion;
+
+/**
+ * Activity custom completion subclass for the assign activity.
+ *
+ * Class for defining mod_assign's custom completion rules and fetching the completion statuses
+ * of the custom completion rules for a given assign instance and a user.
+ *
+ * @package mod_assign
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class custom_completion extends activity_custom_completion {
+
+    /**
+     * Fetches the completion state for a given completion rule.
+     *
+     * @param string $rule The completion rule.
+     * @return int The completion state.
+     */
+    public function get_state(string $rule): int {
+        global $CFG;
+
+        $this->validate_rule($rule);
+
+        $userid = $this->userid;
+        $cm = $this->cm;
+
+        require_once($CFG->dirroot . '/mod/assign/locallib.php');
+
+        $assign = new \assign(null, $cm, $cm->get_course());
+        if ($assign->get_instance()->teamsubmission) {
+            $submission = $assign->get_group_submission($userid, 0, false);
+        } else {
+            $submission = $assign->get_user_submission($userid, false);
+        }
+        $status = $submission && $submission->status == ASSIGN_SUBMISSION_STATUS_SUBMITTED;
+
+        return $status ? COMPLETION_COMPLETE : COMPLETION_INCOMPLETE;
+    }
+
+    /**
+     * Fetch the list of custom completion rules that this module defines.
+     *
+     * @return array
+     */
+    public static function get_defined_custom_rules(): array {
+        return ['completionsubmit'];
+    }
+
+    /**
+     * Returns an associative array of the descriptions of custom completion rules.
+     *
+     * @return array
+     */
+    public function get_custom_rule_descriptions(): array {
+        return [
+            'completionsubmit' => get_string('completiondetail:submit', 'assign')
+        ];
+    }
+}
+
diff --git a/mod/assign/lang/en/assign.php b/mod/assign/lang/en/assign.php
index 2e903c1de0859..728a80726dd10 100644
--- a/mod/assign/lang/en/assign.php
+++ b/mod/assign/lang/en/assign.php
@@ -123,6 +123,7 @@
 $string['collapsegradepanel'] = 'Collapse grade panel';
 $string['collapsereviewpanel'] = 'Collapse review panel';
 $string['comment'] = 'Comment';
+$string['completiondetail:submit'] = 'Make a submission';
 $string['completionsubmit'] = 'Student must submit to this activity to complete it';
 $string['conversionexception'] = 'Could not convert assignment. Exception was: {$a}.';
 $string['configshowrecentsubmissions'] = 'Everyone can see notifications of submissions in recent activity reports.';
diff --git a/mod/assign/tests/custom_completion_test.php b/mod/assign/tests/custom_completion_test.php
new file mode 100644
index 0000000000000..0596257d3e18b
--- /dev/null
+++ b/mod/assign/tests/custom_completion_test.php
@@ -0,0 +1,239 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Contains unit tests for core_completion/activity_custom_completion.
+ *
+ * @package   mod_assign
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+declare(strict_types=1);
+
+namespace mod_assign;
+
+use advanced_testcase;
+use cm_info;
+use coding_exception;
+use mod_assign\completion\custom_completion;
+use moodle_exception;
+
+defined('MOODLE_INTERNAL') || die();
+
+global $CFG;
+require_once($CFG->libdir . '/completionlib.php');
+require_once($CFG->dirroot . '/mod/assign/tests/generator.php');
+/**
+ * Class for unit testing mod_assign/activity_custom_completion.
+ *
+ * @package   mod_assign
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class activity_custom_completion_test extends advanced_testcase {
+
+    // Use the generator helper.
+    use \mod_assign_test_generator;
+
+    /**
+     * Data provider for get_state().
+     *
+     * @return array[]
+     */
+    public function get_state_provider(): array {
+        return [
+            'Undefined rule' => [
+                'somenonexistentrule', COMPLETION_DISABLED, false, null, coding_exception::class
+            ],
+            'Rule not available' => [
+                'completionsubmit', COMPLETION_DISABLED, false, null, moodle_exception::class
+            ],
+            'Rule available, user has not submitted' => [
+                'completionsubmit', COMPLETION_ENABLED, false, COMPLETION_INCOMPLETE, null
+            ],
+            'Rule available, user has submitted' => [
+                'completionsubmit', COMPLETION_ENABLED, true, COMPLETION_COMPLETE, null
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_state().
+     *
+     * @dataProvider get_state_provider
+     * @param string $rule The custom completion rule.
+     * @param int $available Whether this rule is available.
+     * @param bool $submitted
+     * @param int|null $status Expected status.
+     * @param string|null $exception Expected exception.
+     */
+    public function test_get_state(string $rule, int $available, ?bool $submitted, ?int $status, ?string $exception) {
+        if (!is_null($exception)) {
+            $this->expectException($exception);
+        }
+
+        $this->resetAfterTest();
+
+        $course = $this->getDataGenerator()->create_course(['enablecompletion' => 1]);
+        $student = $this->getDataGenerator()->create_and_enrol($course, 'student');
+        $assign = $this->create_instance($course, ['completion' => COMPLETION_TRACKING_AUTOMATIC, $rule => $available]);
+
+        // Submit the assignment as the student.
+        $this->setUser($student);
+        if ($submitted == true) {
+            $this->add_submission($student, $assign);
+            $this->submit_for_grading($student, $assign);
+        }
+        $cm = cm_info::create($assign->get_course_module());
+
+        $customcompletion = new custom_completion($cm, (int)$student->id);
+        $this->assertEquals($status, $customcompletion->get_state($rule));
+    }
+
+    /**
+     * Test for get_state().
+     *
+     * @dataProvider get_state_provider
+     * @param string $rule The custom completion rule.
+     * @param int $available Whether this rule is available.
+     * @param bool $submitted
+     * @param int|null $status Expected status.
+     * @param string|null $exception Expected exception.
+     */
+    public function test_get_state_group(string $rule, int $available, ?bool $submitted, ?int $status, ?string $exception) {
+        if (!is_null($exception)) {
+            $this->expectException($exception);
+        }
+
+        $this->resetAfterTest();
+
+        $course = $this->getDataGenerator()->create_course(['enablecompletion' => 1]);
+        $student = $this->getDataGenerator()->create_and_enrol($course, 'student');
+        $assign = $this->create_instance($course, ['completion' => COMPLETION_TRACKING_AUTOMATIC, $rule => $available,
+                'teamsubmission' => 1]);
+
+        // Submit the assignment as the student.
+        $this->setUser($student);
+        if ($submitted == true) {
+            $this->add_submission($student, $assign);
+            $this->submit_for_grading($student, $assign);
+        }
+        $cm = cm_info::create($assign->get_course_module());
+
+        $customcompletion = new custom_completion($cm, (int)$student->id);
+        $this->assertEquals($status, $customcompletion->get_state($rule));
+    }
+
+
+    /**
+     * Test for get_defined_custom_rules().
+     */
+    public function test_get_defined_custom_rules() {
+        $rules = custom_completion::get_defined_custom_rules();
+        $this->assertCount(1, $rules);
+        $this->assertEquals('completionsubmit', reset($rules));
+    }
+
+    /**
+     * Test for get_defined_custom_rule_descriptions().
+     */
+    public function test_get_custom_rule_descriptions() {
+        $this->resetAfterTest();
+        // Get defined custom rules.
+        $rules = custom_completion::get_defined_custom_rules();
+        // Get custom rule descriptions.
+        $course = $this->getDataGenerator()->create_course(['enablecompletion' => 1]);
+        $assign = $this->create_instance($course, [
+            'submissiondrafts' => 0,
+            'completionusegrade' => 1
+        ]);
+
+        $cm = cm_info::create($assign->get_course_module());
+        $customcompletion = new custom_completion($cm, 1);
+        $ruledescriptions = $customcompletion->get_custom_rule_descriptions();
+
+        // Confirm that defined rules and rule descriptions are consistent with each other.
+        $this->assertEquals(count($rules), count($ruledescriptions));
+        foreach ($rules as $rule) {
+            $this->assertArrayHasKey($rule, $ruledescriptions);
+        }
+    }
+
+    /**
+     * Test for is_defined().
+     */
+    public function test_is_defined() {
+        $this->resetAfterTest();
+        $course = $this->getDataGenerator()->create_course(['enablecompletion' => 1]);
+        $assign = $this->create_instance($course, [
+            'submissiondrafts' => 0,
+            'completionsubmit' => 1
+        ]);
+
+        $cm = cm_info::create($assign->get_course_module());
+
+        $customcompletion = new custom_completion($cm, 1);
+
+        // Rule is defined.
+        $this->assertTrue($customcompletion->is_defined('completionsubmit'));
+
+        // Undefined rule.
+        $this->assertFalse($customcompletion->is_defined('somerandomrule'));
+    }
+
+    /**
+     * Data provider for test_get_available_custom_rules().
+     *
+     * @return array[]
+     */
+    public function get_available_custom_rules_provider(): array {
+        return [
+            'Completion submit available' => [
+                COMPLETION_ENABLED, ['completionsubmit']
+            ],
+            'Completion submit not available' => [
+                COMPLETION_DISABLED, []
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_available_custom_rules().
+     *
+     * @dataProvider get_available_custom_rules_provider
+     * @param int $status
+     * @param array $expected
+     */
+    public function test_get_available_custom_rules(int $status, array $expected) {
+        $this->resetAfterTest();
+        $course = $this->getDataGenerator()->create_course(['enablecompletion' => $status]);
+
+        $params = [];
+        if ($status == COMPLETION_ENABLED ) {
+            $params = [
+                'completion' => COMPLETION_TRACKING_AUTOMATIC,
+                'completionsubmit' => 1
+            ];
+        }
+
+        $assign = $this->create_instance($course, $params);
+        $cm = cm_info::create($assign->get_course_module());
+
+        $customcompletion = new custom_completion($cm, 1);
+        $this->assertEquals($expected, $customcompletion->get_available_custom_rules());
+    }
+}
diff --git a/mod/data/classes/completion/custom_completion.php b/mod/data/classes/completion/custom_completion.php
new file mode 100644
index 0000000000000..4ace7a58e50bd
--- /dev/null
+++ b/mod/data/classes/completion/custom_completion.php
@@ -0,0 +1,72 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+declare(strict_types=1);
+
+namespace mod_data\completion;
+
+use core_completion\activity_custom_completion;
+
+/**
+ * Activity custom completion subclass for the data activity.
+ *
+ * Class for defining mod_data's custom completion rules and fetching the completion statuses
+ * of the custom completion rules for a given data instance and a user.
+ *
+ * @package mod_data
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class custom_completion extends activity_custom_completion {
+
+    /**
+     * Fetches the completion state for a given completion rule.
+     *
+     * @param string $rule The completion rule.
+     * @return int The completion state.
+     */
+    public function get_state(string $rule): int {
+        global $DB;
+
+        $this->validate_rule($rule);
+
+        $userentries = $DB->count_records('data_records', ['dataid' => $this->cm->instance, 'userid' => $this->userid]);
+        $completionentries = $this->cm->customdata['customcompletionrules']['completionentries'];
+
+        return ($completionentries <= $userentries) ? COMPLETION_COMPLETE : COMPLETION_INCOMPLETE;
+    }
+
+    /**
+     * Fetch the list of custom completion rules that this module defines.
+     *
+     * @return array
+     */
+    public static function get_defined_custom_rules(): array {
+        return ['completionentries'];
+    }
+
+    /**
+     * Returns an associative array of the descriptions of custom completion rules.
+     *
+     * @return array
+     */
+    public function get_custom_rule_descriptions(): array {
+        $entries = $this->cm->customdata['customcompletionrules']['completionentries'] ?? 0;
+        return [
+            'completionentries' => get_string('completiondetail:entries', 'data', $entries),
+        ];
+    }
+}
diff --git a/mod/data/lang/en/data.php b/mod/data/lang/en/data.php
index 23c9822f1cd30..4f81b60c09be5 100644
--- a/mod/data/lang/en/data.php
+++ b/mod/data/lang/en/data.php
@@ -71,6 +71,7 @@
 $string['commentsaved'] = 'Comment saved';
 $string['commentsn'] = '{$a} comment(s)';
 $string['commentsoff'] = 'Comments feature is not enabled';
+$string['completiondetail:entries'] = 'Make entries: {$a}';
 $string['completionentries'] = 'Require entries';
 $string['completionentriescount'] = 'Count of entries';
 $string['completionentriesdesc'] = 'Minimum number of entries required: {$a}';
diff --git a/mod/data/tests/custom_completion_test.php b/mod/data/tests/custom_completion_test.php
new file mode 100644
index 0000000000000..8cd39265c54d7
--- /dev/null
+++ b/mod/data/tests/custom_completion_test.php
@@ -0,0 +1,216 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Contains unit tests for core_completion/activity_custom_completion.
+ *
+ * @package   mod_data
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+declare(strict_types=1);
+
+namespace mod_data;
+
+use advanced_testcase;
+use cm_info;
+use coding_exception;
+use mod_data\completion\custom_completion;
+use moodle_exception;
+
+defined('MOODLE_INTERNAL') || die();
+
+global $CFG;
+require_once($CFG->libdir . '/completionlib.php');
+
+/**
+ * Class for unit testing mod_data/activity_custom_completion.
+ *
+ * @package   mod_data
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class custom_completion_test extends advanced_testcase {
+
+    /**
+     * Data provider for get_state().
+     *
+     * @return array[]
+     */
+    public function get_state_provider(): array {
+        return [
+            'Undefined rule' => [
+                'somenonexistentrule', COMPLETION_DISABLED, 0, null, coding_exception::class
+            ],
+            'Rule not available' => [
+                'completionentries', COMPLETION_DISABLED, 0, null, moodle_exception::class
+            ],
+            'Rule available, user has not created entries' => [
+                'completionentries', COMPLETION_ENABLED, 0, COMPLETION_INCOMPLETE, null
+            ],
+            'Rule available, user has created entries' => [
+                'completionentries', COMPLETION_ENABLED, 2, COMPLETION_COMPLETE, null
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_state().
+     *
+     * @dataProvider get_state_provider
+     * @param string $rule The custom completion rule.
+     * @param int $available Whether this rule is available.
+     * @param int $entries The number of entries.
+     * @param int|null $status Expected status.
+     * @param string|null $exception Expected exception.
+     */
+    public function test_get_state(string $rule, int $available, int $entries, ?int $status, ?string $exception) {
+        global $DB;
+
+        if (!is_null($exception)) {
+            $this->expectException($exception);
+        }
+
+        // Custom completion rule data for cm_info::customdata.
+        $customdataval = [
+            'customcompletionrules' => [
+                $rule => $available
+            ]
+        ];
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Mock the return of the magic getter method when fetching the cm_info object's customdata and instance values.
+        $mockcminfo->expects($this->any())
+            ->method('__get')
+            ->will($this->returnValueMap([
+                ['customdata', $customdataval],
+                ['instance', 1],
+            ]));
+
+        // Mock the DB calls.
+        $DB = $this->createMock(get_class($DB));
+        $DB->expects($this->atMost(1))
+            ->method('count_records')
+            ->willReturn($entries);
+
+        $customcompletion = new custom_completion($mockcminfo, 2);
+        $this->assertEquals($status, $customcompletion->get_state($rule));
+    }
+
+    /**
+     * Test for get_defined_custom_rules().
+     */
+    public function test_get_defined_custom_rules() {
+        $rules = custom_completion::get_defined_custom_rules();
+        $this->assertCount(1, $rules);
+        $this->assertEquals('completionentries', reset($rules));
+    }
+
+    /**
+     * Test for get_defined_custom_rule_descriptions().
+     */
+    public function test_get_custom_rule_descriptions() {
+        // Get defined custom rules.
+        $rules = custom_completion::get_defined_custom_rules();
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Instantiate a custom_completion object using the mocked cm_info.
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Get custom rule descriptions.
+        $ruledescriptions = $customcompletion->get_custom_rule_descriptions();
+
+        // Confirm that defined rules and rule descriptions are consistent with each other.
+        $this->assertEquals(count($rules), count($ruledescriptions));
+        foreach ($rules as $rule) {
+            $this->assertArrayHasKey($rule, $ruledescriptions);
+        }
+    }
+
+    /**
+     * Test for is_defined().
+     */
+    public function test_is_defined() {
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Rule is defined.
+        $this->assertTrue($customcompletion->is_defined('completionentries'));
+
+        // Undefined rule.
+        $this->assertFalse($customcompletion->is_defined('somerandomrule'));
+    }
+
+    /**
+     * Data provider for test_get_available_custom_rules().
+     *
+     * @return array[]
+     */
+    public function get_available_custom_rules_provider(): array {
+        return [
+            'Completion entries available' => [
+                COMPLETION_ENABLED, ['completionentries']
+            ],
+            'Completion entries not available' => [
+                COMPLETION_DISABLED, []
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_available_custom_rules().
+     *
+     * @dataProvider get_available_custom_rules_provider
+     * @param int $status
+     * @param array $expected
+     */
+    public function test_get_available_custom_rules(int $status, array $expected) {
+        $customdataval = [
+            'customcompletionrules' => [
+                'completionentries' => $status
+            ]
+        ];
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Mock the return of magic getter for the customdata attribute.
+        $mockcminfo->expects($this->any())
+            ->method('__get')
+            ->with('customdata')
+            ->willReturn($customdataval);
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+        $this->assertEquals($expected, $customcompletion->get_available_custom_rules());
+    }
+}
diff --git a/mod/feedback/classes/completion/custom_completion.php b/mod/feedback/classes/completion/custom_completion.php
new file mode 100644
index 0000000000000..1a17c713a546b
--- /dev/null
+++ b/mod/feedback/classes/completion/custom_completion.php
@@ -0,0 +1,70 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+declare(strict_types=1);
+
+namespace mod_feedback\completion;
+
+use core_completion\activity_custom_completion;
+
+/**
+ * Activity custom completion subclass for the feedback activity.
+ *
+ * Class for defining mod_feedback's custom completion rules and fetching the completion statuses
+ * of the custom completion rules for a given feedback instance and a user.
+ *
+ * @package mod_feedback
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class custom_completion extends activity_custom_completion {
+
+    /**
+     * Fetches the completion state for a given completion rule.
+     *
+     * @param string $rule The completion rule.
+     * @return int The completion state.
+     */
+    public function get_state(string $rule): int {
+        global $DB;
+
+        $this->validate_rule($rule);
+
+        // Feedback only supports completionsubmit as a custom rule.
+        $status = $DB->record_exists('feedback_completed', ['feedback' => $this->cm->instance, 'userid' => $this->userid]);
+        return $status ? COMPLETION_COMPLETE : COMPLETION_INCOMPLETE;
+    }
+
+    /**
+     * Fetch the list of custom completion rules that this module defines.
+     *
+     * @return array
+     */
+    public static function get_defined_custom_rules(): array {
+        return ['completionsubmit'];
+    }
+
+    /**
+     * Returns an associative array of the descriptions of custom completion rules.
+     *
+     * @return array
+     */
+    public function get_custom_rule_descriptions(): array {
+        return [
+            'completionsubmit' => get_string('completiondetail:submit', 'feedback')
+        ];
+    }
+}
diff --git a/mod/feedback/lang/en/feedback.php b/mod/feedback/lang/en/feedback.php
index 49ee6b32a2215..179e5e3e59213 100644
--- a/mod/feedback/lang/en/feedback.php
+++ b/mod/feedback/lang/en/feedback.php
@@ -49,6 +49,7 @@
 $string['complete_the_form'] = 'Answer the questions';
 $string['completed'] = 'Completed';
 $string['completedon'] = 'Completed on {$a}';
+$string['completiondetail:submit'] = 'Submit feedback';
 $string['completionsubmit'] = 'View as completed if the feedback is submitted';
 $string['configallowfullanonymous'] = 'If set to \'yes\', users can complete a feedback activity on the front page without being required to log in.';
 $string['confirmdeleteentry'] = 'Are you sure you want to delete this entry?';
diff --git a/mod/feedback/tests/custom_completion_test.php b/mod/feedback/tests/custom_completion_test.php
new file mode 100644
index 0000000000000..7d0d07ea81784
--- /dev/null
+++ b/mod/feedback/tests/custom_completion_test.php
@@ -0,0 +1,217 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Contains unit tests for core_completion/activity_custom_completion.
+ *
+ * @package   mod_feedback
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+declare(strict_types=1);
+
+namespace mod_feedback;
+
+use advanced_testcase;
+use cm_info;
+use coding_exception;
+use mod_feedback\completion\custom_completion;
+use moodle_exception;
+
+defined('MOODLE_INTERNAL') || die();
+
+global $CFG;
+require_once($CFG->libdir . '/completionlib.php');
+
+/**
+ * Class for unit testing mod_feedback/activity_custom_completion.
+ *
+ * @package   mod_feedback
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class activity_custom_completion_test extends advanced_testcase {
+
+    /**
+     * Data provider for get_state().
+     *
+     * @return array[]
+     */
+    public function get_state_provider(): array {
+        return [
+            'Undefined rule' => [
+                'somenonexistentrule', COMPLETION_DISABLED, false, null, coding_exception::class
+            ],
+            'Rule not available' => [
+                'completionsubmit', COMPLETION_DISABLED, false, null, moodle_exception::class
+            ],
+            'Rule available, user has not submitted' => [
+                'completionsubmit', COMPLETION_ENABLED, false, COMPLETION_INCOMPLETE, null
+            ],
+            'Rule available, user has submitted' => [
+                'completionsubmit', COMPLETION_ENABLED, true, COMPLETION_COMPLETE, null
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_state().
+     *
+     * @dataProvider get_state_provider
+     * @param string $rule The custom completion rule.
+     * @param int $available Whether this rule is available.
+     * @param bool $submitted
+     * @param int|null $status Expected status.
+     * @param string|null $exception Expected exception.
+     */
+    public function test_get_state(string $rule, int $available, ?bool $submitted, ?int $status, ?string $exception) {
+        global $DB;
+
+        if (!is_null($exception)) {
+            $this->expectException($exception);
+        }
+
+        // Custom completion rule data for cm_info::customdata.
+        $customdataval = [
+            'customcompletionrules' => [
+                $rule => $available
+            ]
+        ];
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Mock the return of the magic getter method when fetching the cm_info object's customdata and instance values.
+        $mockcminfo->expects($this->any())
+            ->method('__get')
+            ->will($this->returnValueMap([
+                ['customdata', $customdataval],
+                ['instance', 1],
+            ]));
+
+        // Mock the DB calls.
+        $DB = $this->createMock(get_class($DB));
+        $DB->expects($this->atMost(1))
+            ->method('record_exists')
+            ->willReturn($submitted);
+
+        $customcompletion = new custom_completion($mockcminfo, 2);
+        $this->assertEquals($status, $customcompletion->get_state($rule));
+    }
+
+    /**
+     * Test for get_defined_custom_rules().
+     */
+    public function test_get_defined_custom_rules() {
+        $rules = custom_completion::get_defined_custom_rules();
+        $this->assertCount(1, $rules);
+        $this->assertEquals('completionsubmit', reset($rules));
+    }
+
+    /**
+     * Test for get_defined_custom_rule_descriptions().
+     */
+    public function test_get_custom_rule_descriptions() {
+        // Get defined custom rules.
+        $rules = custom_completion::get_defined_custom_rules();
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Instantiate a custom_completion object using the mocked cm_info.
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Get custom rule descriptions.
+        $ruledescriptions = $customcompletion->get_custom_rule_descriptions();
+
+        // Confirm that defined rules and rule descriptions are consistent with each other.
+        $this->assertEquals(count($rules), count($ruledescriptions));
+        foreach ($rules as $rule) {
+            $this->assertArrayHasKey($rule, $ruledescriptions);
+        }
+    }
+
+    /**
+     * Test for is_defined().
+     */
+    public function test_is_defined() {
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Rule is defined.
+        $this->assertTrue($customcompletion->is_defined('completionsubmit'));
+
+        // Undefined rule.
+        $this->assertFalse($customcompletion->is_defined('somerandomrule'));
+    }
+
+    /**
+     * Data provider for test_get_available_custom_rules().
+     *
+     * @return array[]
+     */
+    public function get_available_custom_rules_provider(): array {
+        return [
+            'Completion submit available' => [
+                COMPLETION_ENABLED, ['completionsubmit']
+            ],
+            'Completion submit not available' => [
+                COMPLETION_DISABLED, []
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_available_custom_rules().
+     *
+     * @dataProvider get_available_custom_rules_provider
+     * @param int $status
+     * @param array $expected
+     */
+    public function test_get_available_custom_rules(int $status, array $expected) {
+        $customdataval = [
+            'customcompletionrules' => [
+                'completionsubmit' => $status
+            ]
+        ];
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Mock the return of magic getter for the customdata attribute.
+        $mockcminfo->expects($this->any())
+            ->method('__get')
+            ->with('customdata')
+            ->willReturn($customdataval);
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+        $this->assertEquals($expected, $customcompletion->get_available_custom_rules());
+    }
+}
diff --git a/mod/forum/classes/completion/custom_completion.php b/mod/forum/classes/completion/custom_completion.php
new file mode 100644
index 0000000000000..b168abd44addb
--- /dev/null
+++ b/mod/forum/classes/completion/custom_completion.php
@@ -0,0 +1,102 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+declare(strict_types=1);
+
+namespace mod_forum\completion;
+
+use core_completion\activity_custom_completion;
+
+/**
+ * Activity custom completion subclass for the forum activity.
+ *
+ * Class for defining mod_forum's custom completion rules and fetching the completion statuses
+ * of the custom completion rules for a given forum instance and a user.
+ *
+ * @package mod_forum
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class custom_completion extends activity_custom_completion {
+
+    /**
+     * Fetches the completion state for a given completion rule.
+     *
+     * @param string $rule The completion rule.
+     * @return int The completion state.
+     */
+    public function get_state(string $rule): int {
+        global $DB;
+
+        $this->validate_rule($rule);
+
+        $userid = $this->userid;
+        $forumid = $this->cm->instance;
+
+        if (!$forum = $DB->get_record('forum', ['id' => $forumid])) {
+            throw new \moodle_exception('Unable to find forum with id ' . $forumid);
+        }
+
+        $postcountparams = ['userid' => $userid, 'forumid' => $forumid];
+        $postcountsql = "SELECT COUNT(*)
+                           FROM {forum_posts} fp
+                           JOIN {forum_discussions} fd ON fp.discussion = fd.id
+                          WHERE fp.userid = :userid
+                            AND fd.forum = :forumid";
+
+        if ($rule == 'completiondiscussions') {
+            $status = $forum->completiondiscussions <=
+                $DB->count_records('forum_discussions', ['forum' => $forumid, 'userid' => $userid]);
+        } else if ($rule == 'completionreplies') {
+            $status = $forum->completionreplies <=
+                $DB->get_field_sql($postcountsql . ' AND fp.parent <> 0', $postcountparams);
+        } else if ($rule == 'completionposts') {
+            $status = $forum->completionposts <= $DB->get_field_sql($postcountsql, $postcountparams);
+        }
+
+        return $status ? COMPLETION_COMPLETE : COMPLETION_INCOMPLETE;
+    }
+
+    /**
+     * Fetch the list of custom completion rules that this module defines.
+     *
+     * @return array
+     */
+    public static function get_defined_custom_rules(): array {
+        return [
+            'completiondiscussions',
+            'completionreplies',
+            'completionposts',
+        ];
+    }
+
+    /**
+     * Returns an associative array of the descriptions of custom completion rules.
+     *
+     * @return array
+     */
+    public function get_custom_rule_descriptions(): array {
+        $completiondiscussions = $this->cm->customdata['customcompletionrules']['completiondiscussions'] ?? 0;
+        $completionreplies = $this->cm->customdata['customcompletionrules']['completionreplies'] ?? 0;
+        $completionposts = $this->cm->customdata['customcompletionrules']['completionposts'] ?? 0;
+
+        return [
+            'completiondiscussions' => get_string('completiondetail:discussions', 'forum', $completiondiscussions),
+            'completionreplies' => get_string('completiondetail:replies', 'forum', $completionreplies),
+            'completionposts' => get_string('completiondetail:posts', 'forum', $completionposts),
+        ];
+    }
+}
diff --git a/mod/forum/lang/en/forum.php b/mod/forum/lang/en/forum.php
index 29dcbf289b388..1e65390357725 100644
--- a/mod/forum/lang/en/forum.php
+++ b/mod/forum/lang/en/forum.php
@@ -104,6 +104,9 @@
 $string['clicktofavourite'] = 'You have not starred this discussion. Click to star.';
 $string['close'] = 'Close';
 $string['closegrader'] = 'Close grader';
+$string['completiondetail:discussions'] = 'Start discussions: {$a}';
+$string['completiondetail:replies'] = 'Post replies: {$a}';
+$string['completiondetail:posts'] = 'Make forum posts: {$a}';
 $string['completiondiscussions'] = 'Student must create discussions:';
 $string['completiondiscussionsdesc'] = 'Student must create at least {$a} discussion(s)';
 $string['completiondiscussionsgroup'] = 'Require discussions';
diff --git a/mod/forum/tests/custom_completion_test.php b/mod/forum/tests/custom_completion_test.php
new file mode 100644
index 0000000000000..0f7fd08085445
--- /dev/null
+++ b/mod/forum/tests/custom_completion_test.php
@@ -0,0 +1,273 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Contains unit tests for core_completion/activity_custom_completion.
+ *
+ * @package   mod_forum
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+declare(strict_types=1);
+
+namespace mod_forum;
+
+use advanced_testcase;
+use cm_info;
+use coding_exception;
+use mod_forum\completion\custom_completion;
+use moodle_exception;
+
+defined('MOODLE_INTERNAL') || die();
+
+global $CFG;
+require_once($CFG->libdir . '/completionlib.php');
+require_once($CFG->dirroot . '/mod/forum/tests/generator/lib.php');
+require_once($CFG->dirroot . '/mod/forum/tests/generator_trait.php');
+
+/**
+ * Class for unit testing mod_forum/activity_custom_completion.
+ *
+ * @package   mod_forum
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class custom_completion_test extends advanced_testcase {
+
+    use \mod_forum_tests_generator_trait;
+
+    /**
+     * Data provider for get_state().
+     *
+     * @return array[]
+     */
+    public function get_state_provider(): array {
+        return [
+            'Undefined rule' => [
+                'somenonexistentrule', 0, COMPLETION_TRACKING_NONE, 0, 0, 0, null, coding_exception::class
+            ],
+            'Completion discussions rule not available'  => [
+                'completiondiscussions', 0,  COMPLETION_TRACKING_NONE, 0, 0, 0, null, moodle_exception::class
+            ],
+            'Completion discussions rule available, user has not created discussion' => [
+                'completiondiscussions', 0, COMPLETION_TRACKING_AUTOMATIC, 5, 0, 0, COMPLETION_INCOMPLETE, null
+            ],
+            'Rule available, user has created discussions' => [
+                'completiondiscussions', 5, COMPLETION_TRACKING_AUTOMATIC, 5, 0, 0, COMPLETION_COMPLETE, null
+            ],
+            'Completion replies rule not available' => [
+                'completionreplies', 0, COMPLETION_TRACKING_NONE, 0, 0, 0, null, moodle_exception::class
+            ],
+            'Rule available, user has not replied' => [
+                'completionreplies', 0, COMPLETION_TRACKING_AUTOMATIC, 0, 5, 0, COMPLETION_INCOMPLETE, null
+            ],
+            'Rule available, user has created replied' => [
+                'completionreplies', 5, COMPLETION_TRACKING_AUTOMATIC, 0, 5, 0, COMPLETION_COMPLETE, null
+            ],
+            'Completion posts rule not available' => [
+                'completionposts', 0, COMPLETION_TRACKING_NONE, 0, 0, 0, null, moodle_exception::class
+            ],
+            'Rule available, user has not posted' => [
+                'completionposts', 0, COMPLETION_TRACKING_AUTOMATIC, 0, 0, 5, COMPLETION_INCOMPLETE, null
+            ],
+            'Rule available, user has posted' => [
+                'completionposts', 5, COMPLETION_TRACKING_AUTOMATIC, 0, 0, 5, COMPLETION_COMPLETE, null
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_state().
+     *
+     * @dataProvider get_state_provider
+     * @param string $rule The custom completion rule.
+     * @param int $rulecount Quantity of discussions, replies or posts to be created.
+     * @param int $available Whether this rule is available.
+     * @param int|null $discussions The number of discussions.
+     * @param int|null $replies The number of replies.
+     * @param int|null $posts The number of posts.
+     * @param int|null $status Expected status.
+     * @param string|null $exception Expected exception.
+     */
+    public function test_get_state(string $rule, int $rulecount, int $available, ?int $discussions, ?int $replies,
+                                   ?int $posts, ?int $status, ?string $exception) {
+
+        if (!is_null($exception)) {
+            $this->expectException($exception);
+        }
+
+        $this->resetAfterTest();
+
+        $course = $this->getDataGenerator()->create_course(['enablecompletion' => COMPLETION_ENABLED]);
+        $student = $this->getDataGenerator()->create_and_enrol($course, 'student');
+
+        $forumgenerator = $this->getDataGenerator()->get_plugin_generator('mod_forum');
+
+        $params = [
+            'course' => $course->id,
+            'completion' => $available,
+            'completiondiscussions' => $discussions,
+            'completionreplies' => $replies,
+            'completionposts' => $posts
+        ];
+        $forum = $this->getDataGenerator()->create_module('forum', $params);
+
+        $cm = get_coursemodule_from_instance('forum', $forum->id);
+
+        if ($rulecount > 0) {
+            if ($rule == 'completiondiscussions') {
+                // Create x number of discussions.
+                for ($i = 0; $i < $rulecount; $i++) {
+                    $forumgenerator->create_discussion((object) [
+                        'course' => $forum->course,
+                        'userid' => $student->id,
+                        'forum' => $forum->id,
+                    ]);
+                }
+            } else if ($rule == 'completionreplies') {
+                [$discussion1, $post1] = $this->helper_post_to_forum($forum, $student);
+                for ($i = 0; $i < $rulecount; $i++) {
+                    $this->helper_reply_to_post($post1, $student);
+                }
+            } else if ($rule == 'completionposts') {
+                for ($i = 0; $i < $rulecount; $i++) {
+                    $this->helper_post_to_forum($forum, $student);
+                }
+            }
+        }
+
+        // Make sure we're using a cm_info object.
+        $cm = cm_info::create($cm);
+
+        $customcompletion = new custom_completion($cm, (int)$student->id);
+        $this->assertEquals($status, $customcompletion->get_state($rule));
+    }
+
+    /**
+     * Test for get_defined_custom_rules().
+     */
+    public function test_get_defined_custom_rules() {
+        $rules = custom_completion::get_defined_custom_rules();
+        $this->assertCount(3, $rules);
+        $this->assertEquals('completiondiscussions', reset($rules));
+    }
+
+    /**
+     * Test for get_defined_custom_rule_descriptions().
+     */
+    public function test_get_custom_rule_descriptions() {
+        // Get defined custom rules.
+        $rules = custom_completion::get_defined_custom_rules();
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+        // Instantiate a custom_completion object using the mocked cm_info.
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Get custom rule descriptions.
+        $ruledescriptions = $customcompletion->get_custom_rule_descriptions();
+
+        // Confirm that defined rules and rule descriptions are consistent with each other.
+        $this->assertEquals(count($rules), count($ruledescriptions));
+        foreach ($rules as $rule) {
+            $this->assertArrayHasKey($rule, $ruledescriptions);
+        }
+    }
+
+    /**
+     * Test for is_defined().
+     */
+    public function test_is_defined() {
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Rule is defined.
+        $this->assertTrue($customcompletion->is_defined('completiondiscussions'));
+
+        // Undefined rule.
+        $this->assertFalse($customcompletion->is_defined('somerandomrule'));
+    }
+
+    /**
+     * Data provider for test_get_available_custom_rules().
+     *
+     * @return array[]
+     */
+    public function get_available_custom_rules_provider(): array {
+        return [
+            'Completion discussions available' => [
+                COMPLETION_ENABLED, ['completiondiscussions']
+            ],
+            'Completion discussions not available' => [
+                COMPLETION_DISABLED, []
+            ],
+            'Completion replies available' => [
+                COMPLETION_ENABLED, ['completionreplies']
+            ],
+            'Completion replies not available' => [
+                COMPLETION_DISABLED, []
+            ],
+            'Completion posts available' => [
+                COMPLETION_ENABLED, ['completionposts']
+            ],
+            'Completion posts not available' => [
+                COMPLETION_DISABLED, []
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_available_custom_rules().
+     *
+     * @dataProvider get_available_custom_rules_provider
+     * @param int $status
+     * @param array $expected
+     */
+    public function test_get_available_custom_rules(int $status, array $expected) {
+        $customdataval = [
+            'customcompletionrules' => []
+        ];
+        if ($status == COMPLETION_ENABLED) {
+            $rule = $expected[0];
+            $customdataval = [
+                'customcompletionrules' => [$rule => $status]
+            ];
+        }
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Mock the return of magic getter for the customdata attribute.
+        $mockcminfo->expects($this->any())
+            ->method('__get')
+            ->with('customdata')
+            ->willReturn($customdataval);
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+        $this->assertEquals($expected, $customcompletion->get_available_custom_rules());
+    }
+}
diff --git a/mod/glossary/classes/completion/custom_completion.php b/mod/glossary/classes/completion/custom_completion.php
new file mode 100644
index 0000000000000..60deecbea2398
--- /dev/null
+++ b/mod/glossary/classes/completion/custom_completion.php
@@ -0,0 +1,76 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+declare(strict_types=1);
+
+namespace mod_glossary\completion;
+
+use core_completion\activity_custom_completion;
+
+/**
+ * Activity custom completion subclass for the glossary activity.
+ *
+ * Class for defining mod_glossary's custom completion rules and fetching the completion statuses
+ * of the custom completion rules for a given glossary instance and a user.
+ *
+ * @package mod_glossary
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class custom_completion extends activity_custom_completion {
+
+    /**
+     * Fetches the completion state for a given completion rule.
+     *
+     * @param string $rule The completion rule.
+     * @return int The completion state.
+     */
+    public function get_state(string $rule): int {
+        global $DB;
+
+        $this->validate_rule($rule);
+
+        $glossaryid = $this->cm->instance;
+        $userid = $this->userid;
+
+        $userentries = $DB->count_records('glossary_entries', ['glossaryid' => $glossaryid, 'userid' => $userid,
+                'approved' => 1]);
+        $completionentries = $this->cm->customdata['customcompletionrules']['completionentries'];
+
+        return ($completionentries <= $userentries) ? COMPLETION_COMPLETE : COMPLETION_INCOMPLETE;
+    }
+
+    /**
+     * Fetch the list of custom completion rules that this module defines.
+     *
+     * @return array
+     */
+    public static function get_defined_custom_rules(): array {
+        return ['completionentries'];
+    }
+
+    /**
+     * Returns an associative array of the descriptions of custom completion rules.
+     *
+     * @return array
+     */
+    public function get_custom_rule_descriptions(): array {
+        $completionentries = $this->cm->customdata['customcompletionrules']['completionentries'] ?? 0;
+        return [
+            'completionentries' => get_string('completiondetail:entries', 'glossary', $completionentries),
+        ];
+    }
+}
diff --git a/mod/glossary/lang/en/glossary.php b/mod/glossary/lang/en/glossary.php
index 42ab670629fc1..0e64b5618857c 100644
--- a/mod/glossary/lang/en/glossary.php
+++ b/mod/glossary/lang/en/glossary.php
@@ -87,6 +87,7 @@
 $string['comments'] = 'Comments';
 $string['commentson'] = 'Comments on';
 $string['commentupdated'] = 'The comment has been updated.';
+$string['completiondetail:entries'] = 'Make entries: {$a}';
 $string['completionentries'] = 'Student must create entries:';
 $string['completionentriesdesc'] = 'Student must create at least {$a} entry/entries';
 $string['completionentriesgroup'] = 'Require entries';
diff --git a/mod/glossary/tests/custom_completion_test.php b/mod/glossary/tests/custom_completion_test.php
new file mode 100644
index 0000000000000..c9af3d71cd76e
--- /dev/null
+++ b/mod/glossary/tests/custom_completion_test.php
@@ -0,0 +1,217 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Contains unit tests for core_completion/activity_custom_completion.
+ *
+ * @package   mod_glossary
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+declare(strict_types=1);
+
+namespace mod_glossary;
+
+use advanced_testcase;
+use cm_info;
+use coding_exception;
+use mod_glossary\completion\custom_completion;
+use moodle_exception;
+
+defined('MOODLE_INTERNAL') || die();
+
+global $CFG;
+require_once($CFG->libdir . '/completionlib.php');
+
+/**
+ * Class for unit testing mod_glossary/activity_custom_completion.
+ *
+ * @package   mod_glossary
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class custom_completion_test extends advanced_testcase {
+
+    /**
+     * Data provider for get_state().
+     *
+     * @return array[]
+     */
+    public function get_state_provider(): array {
+        return [
+            'Undefined rule' => [
+                'somenonexistentrule', COMPLETION_DISABLED, 0, null, coding_exception::class
+            ],
+            'Rule not available' => [
+                'completionentries', COMPLETION_DISABLED, 0, null, moodle_exception::class
+            ],
+            'Rule available, user has not submitted' => [
+                'completionentries', COMPLETION_ENABLED, 0, COMPLETION_INCOMPLETE, null
+            ],
+            'Rule available, user has submitted' => [
+                'completionentries', COMPLETION_ENABLED, 2, COMPLETION_COMPLETE, null
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_state().
+     *
+     * @dataProvider get_state_provider
+     * @param string $rule The custom completion rule.
+     * @param int $available Whether this rule is available.
+     * @param int $entries The number of entries.
+     * @param int|null $status Expected status.
+     * @param string|null $exception Expected exception.
+     */
+    public function test_get_state(string $rule, int $available, int $entries, ?int $status, ?string $exception) {
+        global $DB;
+
+        if (!is_null($exception)) {
+            $this->expectException($exception);
+        }
+
+        // Custom completion rule data for cm_info::customdata.
+        $customdataval = [
+            'customcompletionrules' => [
+                $rule => $available
+            ]
+        ];
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Mock the return of the magic getter method when fetching the cm_info object's customdata and instance values.
+        $mockcminfo->expects($this->any())
+            ->method('__get')
+            ->will($this->returnValueMap([
+                ['customdata', $customdataval],
+                ['instance', 1],
+            ]));
+
+        // Mock the DB calls.
+        $DB = $this->createMock(get_class($DB));
+        $DB->expects($this->atMost(1))
+            ->method('count_records')
+            ->willReturn($entries);
+
+        $customcompletion = new custom_completion($mockcminfo, 2);
+        $this->assertEquals($status, $customcompletion->get_state($rule));
+    }
+
+    /**
+     * Test for get_defined_custom_rules().
+     */
+    public function test_get_defined_custom_rules() {
+        $rules = custom_completion::get_defined_custom_rules();
+        $this->assertCount(1, $rules);
+        $this->assertEquals('completionentries', $rules[0]);
+    }
+
+    /**
+     * Test for get_defined_custom_rule_descriptions().
+     */
+    public function test_get_custom_rule_descriptions() {
+        // Get defined custom rules.
+        $rules = custom_completion::get_defined_custom_rules();
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Instantiate a custom_completion object using the mocked cm_info.
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Get custom rule descriptions.
+        $ruledescriptions = $customcompletion->get_custom_rule_descriptions();
+
+        // Confirm that defined rules and rule descriptions are consistent with each other.
+        $this->assertEquals(count($rules), count($ruledescriptions));
+        foreach ($rules as $rule) {
+            $this->assertArrayHasKey($rule, $ruledescriptions);
+        }
+    }
+
+    /**
+     * Test for is_defined().
+     */
+    public function test_is_defined() {
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Rule is defined.
+        $this->assertTrue($customcompletion->is_defined('completionentries'));
+
+        // Undefined rule.
+        $this->assertFalse($customcompletion->is_defined('somerandomrule'));
+    }
+
+    /**
+     * Data provider for test_get_available_custom_rules().
+     *
+     * @return array[]
+     */
+    public function get_available_custom_rules_provider(): array {
+        return [
+            'Completion submit available' => [
+                COMPLETION_ENABLED, ['completionentries']
+            ],
+            'Completion submit not available' => [
+                COMPLETION_DISABLED, []
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_available_custom_rules().
+     *
+     * @dataProvider get_available_custom_rules_provider
+     * @param int $status
+     * @param array $expected
+     */
+    public function test_get_available_custom_rules(int $status, array $expected) {
+        $customdataval = [
+            'customcompletionrules' => [
+                'completionentries' => $status
+            ]
+        ];
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Mock the return of magic getter for the customdata attribute.
+        $mockcminfo->expects($this->any())
+            ->method('__get')
+            ->with('customdata')
+            ->willReturn($customdataval);
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+        $this->assertEquals($expected, $customcompletion->get_available_custom_rules());
+    }
+}
diff --git a/mod/survey/classes/completion/custom_completion.php b/mod/survey/classes/completion/custom_completion.php
new file mode 100644
index 0000000000000..27819934d7b11
--- /dev/null
+++ b/mod/survey/classes/completion/custom_completion.php
@@ -0,0 +1,70 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+declare(strict_types=1);
+
+namespace mod_survey\completion;
+
+use core_completion\activity_custom_completion;
+
+/**
+ * Activity custom completion subclass for the survey activity.
+ *
+ * Class for defining mod_survey's custom completion rules and fetching the completion statuses
+ * of the custom completion rules for a given survey instance and a user.
+ *
+ * @package mod_survey
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class custom_completion extends activity_custom_completion {
+
+    /**
+     * Fetches the completion state for a given completion rule.
+     *
+     * @param string $rule The completion rule.
+     * @return int The completion state.
+     */
+    public function get_state(string $rule): int {
+        global $DB;
+
+        $this->validate_rule($rule);
+
+        // Survey only supports completionsubmit as a custom rule.
+        $status = $DB->record_exists('survey_answers', ['survey' => $this->cm->instance, 'userid' => $this->userid]);
+        return $status ? COMPLETION_COMPLETE : COMPLETION_INCOMPLETE;
+    }
+
+    /**
+     * Fetch the list of custom completion rules that this module defines.
+     *
+     * @return array
+     */
+    public static function get_defined_custom_rules(): array {
+        return ['completionsubmit'];
+    }
+
+    /**
+     * Returns an associative array of the descriptions of custom completion rules.
+     *
+     * @return array
+     */
+    public function get_custom_rule_descriptions(): array {
+        return [
+            'completionsubmit' => get_string('completiondetail:submit', 'survey')
+        ];
+    }
+}
diff --git a/mod/survey/lang/en/survey.php b/mod/survey/lang/en/survey.php
index 138d3bb659640..3d0321cc2dac1 100644
--- a/mod/survey/lang/en/survey.php
+++ b/mod/survey/lang/en/survey.php
@@ -82,6 +82,7 @@
 $string['cannotfindanswer'] = 'There are no answers for this survey yet.';
 $string['cannotfindquestion'] = 'Question doesn\'t exist';
 $string['cannotfindsurveytmpt'] = 'No survey templates found!';
+$string['completiondetail:submit'] = 'Submit answers';
 $string['completionsubmit'] = 'Student must submit to this activity to complete it';
 $string['ciqintro'] = 'While thinking about recent events in this class, answer the questions below.';
 $string['ciqname'] = 'Critical incidents';
diff --git a/mod/survey/tests/custom_completion_test.php b/mod/survey/tests/custom_completion_test.php
new file mode 100644
index 0000000000000..6457e7c563f9e
--- /dev/null
+++ b/mod/survey/tests/custom_completion_test.php
@@ -0,0 +1,217 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Contains unit tests for core_completion/activity_custom_completion.
+ *
+ * @package   mod_survey
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+declare(strict_types=1);
+
+namespace mod_survey;
+
+use advanced_testcase;
+use cm_info;
+use coding_exception;
+use mod_survey\completion\custom_completion;
+use moodle_exception;
+
+defined('MOODLE_INTERNAL') || die();
+
+global $CFG;
+require_once($CFG->libdir . '/completionlib.php');
+
+/**
+ * Class for unit testing mod_survey/activity_custom_completion.
+ *
+ * @package   mod_survey
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class activity_custom_completion_test extends advanced_testcase {
+
+    /**
+     * Data provider for get_state().
+     *
+     * @return array[]
+     */
+    public function get_state_provider(): array {
+        return [
+            'Undefined rule' => [
+                'somenonexistentrule', COMPLETION_DISABLED, false, null, coding_exception::class
+            ],
+            'Rule not available' => [
+                'completionsubmit', COMPLETION_DISABLED, false, null, moodle_exception::class
+            ],
+            'Rule available, user has not submitted' => [
+                'completionsubmit', COMPLETION_ENABLED, false, COMPLETION_INCOMPLETE, null
+            ],
+            'Rule available, user has submitted' => [
+                'completionsubmit', COMPLETION_ENABLED, true, COMPLETION_COMPLETE, null
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_state().
+     *
+     * @dataProvider get_state_provider
+     * @param string $rule The custom completion rule.
+     * @param int $available Whether this rule is available.
+     * @param bool $submitted
+     * @param int|null $status Expected status.
+     * @param string|null $exception Expected exception.
+     */
+    public function test_get_state(string $rule, int $available, ?bool $submitted, ?int $status, ?string $exception) {
+        global $DB;
+
+        if (!is_null($exception)) {
+            $this->expectException($exception);
+        }
+
+        // Custom completion rule data for cm_info::customdata.
+        $customdataval = [
+            'customcompletionrules' => [
+                $rule => $available
+            ]
+        ];
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Mock the return of the magic getter method when fetching the cm_info object's customdata and instance values.
+        $mockcminfo->expects($this->any())
+            ->method('__get')
+            ->will($this->returnValueMap([
+                ['customdata', $customdataval],
+                ['instance', 1],
+            ]));
+
+        // Mock the DB calls.
+        $DB = $this->createMock(get_class($DB));
+        $DB->expects($this->atMost(1))
+            ->method('record_exists')
+            ->willReturn($submitted);
+
+        $customcompletion = new custom_completion($mockcminfo, 2);
+        $this->assertEquals($status, $customcompletion->get_state($rule));
+    }
+
+    /**
+     * Test for get_defined_custom_rules().
+     */
+    public function test_get_defined_custom_rules() {
+        $rules = custom_completion::get_defined_custom_rules();
+        $this->assertCount(1, $rules);
+        $this->assertEquals('completionsubmit', reset($rules));
+    }
+
+    /**
+     * Test for get_defined_custom_rule_descriptions().
+     */
+    public function test_get_custom_rule_descriptions() {
+        // Get defined custom rules.
+        $rules = custom_completion::get_defined_custom_rules();
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Instantiate a custom_completion object using the mocked cm_info.
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Get custom rule descriptions.
+        $ruledescriptions = $customcompletion->get_custom_rule_descriptions();
+
+        // Confirm that defined rules and rule descriptions are consistent with each other.
+        $this->assertEquals(count($rules), count($ruledescriptions));
+        foreach ($rules as $rule) {
+            $this->assertArrayHasKey($rule, $ruledescriptions);
+        }
+    }
+
+    /**
+     * Test for is_defined().
+     */
+    public function test_is_defined() {
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Rule is defined.
+        $this->assertTrue($customcompletion->is_defined('completionsubmit'));
+
+        // Undefined rule.
+        $this->assertFalse($customcompletion->is_defined('somerandomrule'));
+    }
+
+    /**
+     * Data provider for test_get_available_custom_rules().
+     *
+     * @return array[]
+     */
+    public function get_available_custom_rules_provider(): array {
+        return [
+            'Completion submit available' => [
+                COMPLETION_ENABLED, ['completionsubmit']
+            ],
+            'Completion submit not available' => [
+                COMPLETION_DISABLED, []
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_available_custom_rules().
+     *
+     * @dataProvider get_available_custom_rules_provider
+     * @param int $status
+     * @param array $expected
+     */
+    public function test_get_available_custom_rules(int $status, array $expected) {
+        $customdataval = [
+            'customcompletionrules' => [
+                'completionsubmit' => $status
+            ]
+        ];
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Mock the return of magic getter for the customdata attribute.
+        $mockcminfo->expects($this->any())
+            ->method('__get')
+            ->with('customdata')
+            ->willReturn($customdataval);
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+        $this->assertEquals($expected, $customcompletion->get_available_custom_rules());
+    }
+}