diff --git a/src/editor/Core/Actions.re b/src/editor/Core/Actions.re
index 345e628c21..2c3f65802b 100644
--- a/src/editor/Core/Actions.re
+++ b/src/editor/Core/Actions.re
@@ -4,10 +4,10 @@
  * Encapsulates actions that can impact the editor state
  */
 
-open State;
 open Types;
 
 type t =
+  | BufferUpdate(BufferUpdate.t)
   | ChangeMode(Mode.t)
   | SetEditorFont(EditorFont.t)
   | Noop;
diff --git a/src/editor/Core/Buffer.re b/src/editor/Core/Buffer.re
index cf868263d6..73d1d08297 100644
--- a/src/editor/Core/Buffer.re
+++ b/src/editor/Core/Buffer.re
@@ -4,6 +4,8 @@
  * In-memory text buffer representation
  */
 
+open Types;
+
 type t = {
   file: option(string),
   lines: array(string),
@@ -13,3 +15,43 @@ let ofLines = (lines: array(string)) => {
   let ret: t = {file: None, lines};
   ret;
 };
+
+let slice = (~lines: array(string), ~start, ~length, ()) => {
+  let len = Array.length(lines);
+  if (start >= len) {
+    [||];
+  } else {
+    let len = min(start + length, len) - start;
+    if (len <= 0) {
+      [||];
+    } else {
+      Array.sub(lines, start, len);
+    };
+  };
+};
+
+let applyUpdate = (lines: array(string), update: BufferUpdate.t) => {
+
+    if (update.endLine <= update.startLine) {
+        Array.of_list(update.lines)
+    } else {
+
+  let prev = slice(~lines, ~start=0, ~length=update.startLine, ());
+  let post =
+    slice(
+      ~lines,
+      ~start=update.endLine,
+      ~length=Array.length(lines) - update.endLine,
+      (),
+    );
+
+  let lines = Array.of_list(update.lines);
+
+  Array.concat([prev, lines, post]);
+    }
+};
+
+let update = (buf: t, update: BufferUpdate.t) => {
+  let ret: t = {...buf, lines: applyUpdate(buf.lines, update)};
+  ret;
+};
diff --git a/src/editor/Core/Reducer.re b/src/editor/Core/Reducer.re
index e6fa492c26..34fd6967ea 100644
--- a/src/editor/Core/Reducer.re
+++ b/src/editor/Core/Reducer.re
@@ -12,6 +12,7 @@ let reduce: (State.t, Actions.t) => State.t =
     | ChangeMode(m) =>
       let ret: State.t = {...s, mode: m};
       ret;
+    | BufferUpdate(bu) => {...s, buffer: Buffer.update(s.buffer, bu)}
     | SetEditorFont(font) => {...s, editorFont: font}
     | Noop => s
     };
diff --git a/src/editor/Core/State.re b/src/editor/Core/State.re
index 023801435b..7534a12606 100644
--- a/src/editor/Core/State.re
+++ b/src/editor/Core/State.re
@@ -5,21 +5,6 @@
  */
 
 open Types;
-
-module Mode = {
-  type t =
-    | Insert
-    | Normal
-    | Other;
-
-  let show = v =>
-    switch (v) {
-    | Insert => "insert"
-    | Normal => "normal"
-    | Other => "unknown"
-    };
-};
-
 module Tab = {
   type t = {
     id: int,
@@ -33,12 +18,14 @@ module Tab = {
 type t = {
   mode: Mode.t,
   tabs: list(Tab.t),
+  buffer: Buffer.t,
   editorFont: EditorFont.t,
 };
 
 let create: unit => t =
   () => {
     mode: Insert,
+    buffer: Buffer.ofLines([|"testing"|]),
     editorFont:
       EditorFont.create(
         ~fontFile="FiraCode-Regular.ttf",
diff --git a/src/editor/Core/Types.re b/src/editor/Core/Types.re
index c121b42d11..2b275507b2 100644
--- a/src/editor/Core/Types.re
+++ b/src/editor/Core/Types.re
@@ -10,6 +10,34 @@ module Position = {
     };
 };
 
+module Mode = {
+  type t =
+    | Insert
+    | Normal
+    | Other;
+
+  let show = v =>
+    switch (v) {
+    | Insert => "insert"
+    | Normal => "normal"
+    | Other => "unknown"
+    };
+};
+
+module BufferUpdate = {
+  type t = {
+    startLine: int,
+    endLine: int,
+    lines: list(string),
+  };
+
+  let create = (~startLine, ~endLine, ~lines, ()) => {
+    startLine,
+    endLine,
+    lines,
+  };
+};
+
 module EditorFont = {
   type t = {
     fontFile: string,
diff --git a/src/editor/UI/EditorSurface.re b/src/editor/UI/EditorSurface.re
index 4b5df2e0c6..401bdb9ee8 100644
--- a/src/editor/UI/EditorSurface.re
+++ b/src/editor/UI/EditorSurface.re
@@ -69,12 +69,7 @@ let make = (state: State.t) =>
   component((_slots: React.Hooks.empty) => {
     let theme = Theme.get();
 
-    let bufferView =
-      Buffer.ofLines([|
-        "- Hello from line 1",
-        "- Hello from line 2",
-        "--- Hello from line 3",
-      |])
+    let bufferView = state.buffer
       |> TokenizedBuffer.ofBuffer
       |> TokenizedBufferView.ofTokenizedBuffer;
 
@@ -91,7 +86,6 @@ let make = (state: State.t) =>
         color(theme.foreground),
         flexGrow(1),
       ];
-    /* flexShrink(1), */
 
     <View style> ...textElements </View>;
   });
diff --git a/src/editor/UI/StatusBar.re b/src/editor/UI/StatusBar.re
index 6229df7129..d367a1cdaa 100644
--- a/src/editor/UI/StatusBar.re
+++ b/src/editor/UI/StatusBar.re
@@ -25,10 +25,10 @@ let viewStyle =
     alignItems(`Center),
   ];
 
-let make = (~mode: State.Mode.t, ()) =>
+let make = (~mode: Types.Mode.t, ()) =>
   component((_slots: React.Hooks.empty) =>
     <View style=viewStyle>
-      <Text style=textStyle text={State.Mode.show(mode)} />
+      <Text style=textStyle text={Types.Mode.show(mode)} />
     </View>
   );
 
diff --git a/src/editor/bin/Oni2.re b/src/editor/bin/Oni2.re
index c808ed3b0f..31dd2e9c6c 100644
--- a/src/editor/bin/Oni2.re
+++ b/src/editor/bin/Oni2.re
@@ -40,7 +40,7 @@ let init = app => {
     let state: Core.State.t = App.getState(app);
     prerr_endline(
       "[DEBUG - STATE] Mode: "
-      ++ Core.State.Mode.show(state.mode)
+      ++ Core.Types.Mode.show(state.mode)
       ++ " editor font measured width: "
       ++ string_of_int(state.editorFont.measuredWidth)
       ++ " editor font measured height: "
@@ -154,6 +154,7 @@ let init = app => {
           | ModeChanged("normal") => Core.Actions.ChangeMode(Normal)
           | ModeChanged("insert") => Core.Actions.ChangeMode(Insert)
           | ModeChanged(_) => Core.Actions.ChangeMode(Other)
+          | BufferLines(bc) => Core.Actions.BufferUpdate(Core.Types.BufferUpdate.create(~startLine=bc.firstLine, ~endLine=bc.lastLine, ~lines=bc.lines, ()))
           | _ => Noop
           };
 
diff --git a/test/editor/Core/BufferTests.re b/test/editor/Core/BufferTests.re
new file mode 100644
index 0000000000..14507fc345
--- /dev/null
+++ b/test/editor/Core/BufferTests.re
@@ -0,0 +1,37 @@
+/* open Oni_Core; */
+open TestFramework;
+
+open Helpers;
+
+open Oni_Core.Types;
+module Buffer = Oni_Core.Buffer;
+
+describe("update", ({test, _}) => {
+  test("empty buffer w/ update", ({expect}) => {
+    let buffer = Buffer.ofLines([||]);
+    let update = BufferUpdate.create(~startLine=0, ~endLine=1, ~lines=["a"], ());
+    let updatedBuffer = Buffer.update(buffer, update);
+    validateBuffer(expect, updatedBuffer, [|"a"|]);
+  });
+
+  test("update single line", ({expect}) => {
+    let buffer = Buffer.ofLines([|"a"|]);
+    let update = BufferUpdate.create(~startLine=0, ~endLine=1, ~lines=["abc"], ());
+    let updatedBuffer = Buffer.update(buffer, update);
+    validateBuffer(expect, updatedBuffer, [|"abc"|]);
+  });
+
+  test("delete line", ({expect}) => {
+    let buffer = Buffer.ofLines([|"a"|]);
+    let update = BufferUpdate.create(~startLine=0, ~endLine=1, ~lines=[], ());
+    let updatedBuffer = Buffer.update(buffer, update);
+    validateBuffer(expect, updatedBuffer, [||]);
+  });
+
+  test("update single line", ({expect}) => {
+    let buffer = Buffer.ofLines([|"a", "b", "c"|]);
+    let update = BufferUpdate.create(~startLine=1, ~endLine=2, ~lines=["d", "e", "f"], ());
+    let updatedBuffer = Buffer.update(buffer, update);
+    validateBuffer(expect, updatedBuffer, [|"a", "d", "e", "f", "c"|]);
+  });
+});
diff --git a/test/editor/Core/Helpers.re b/test/editor/Core/Helpers.re
index 1534401b14..eb4c597008 100644
--- a/test/editor/Core/Helpers.re
+++ b/test/editor/Core/Helpers.re
@@ -1,6 +1,8 @@
 open Oni_Core;
 open Oni_Core.Types;
 
+module Buffer = Oni_Core.Buffer;
+
 let validateToken =
     (
       expect: Rely__DefaultMatchers.matchers(unit),
@@ -30,3 +32,22 @@ let validateTokens =
 
   List.iter2(f, actualTokens, expectedTokens);
 };
+
+let validateBuffer =
+    (
+      expect: Rely__DefaultMatchers.matchers(unit),
+      actualBuffer: Buffer.t,
+      expectedLines: array(string),
+    ) => {
+  expect.int(Array.length(actualBuffer.lines)).toBe(Array.length(expectedLines));
+
+  let validateLine = (actualLine, expectedLine) => {
+    expect.string(actualLine).toEqual(expectedLine);
+  }
+
+  let f = (actual, expected) => {
+    validateLine(actual, expected);
+  };
+
+  Array.iter2(f, actualBuffer.lines, expectedLines);
+};