diff --git a/spec/atom/buffer-spec.coffee b/spec/atom/buffer-spec.coffee
index b58a37655..e22c3d43b 100644
--- a/spec/atom/buffer-spec.coffee
+++ b/spec/atom/buffer-spec.coffee
@@ -102,6 +102,24 @@ describe 'Buffer', ->
           expect(buffer.getLine(3)).toBe "    var pivot = sort(Array.apply(this, arguments));"
           expect(buffer.getLine(4)).toBe "};"
 
+  describe ".setText(text)", ->
+    it "changes the entire contents of the buffer and emits a change event", ->
+      lastRow = buffer.lastRow()
+      expectedPreRange = new Range([0,0], [lastRow, buffer.getLine(lastRow).length])
+      changeHandler = jasmine.createSpy('changeHandler')
+      buffer.on 'change', changeHandler
+
+      newText = "I know you are.\nBut what am I?"
+      buffer.setText(newText)
+
+      expect(buffer.getText()).toBe newText
+      expect(changeHandler).toHaveBeenCalled()
+
+      [event] = changeHandler.argsForCall[0]
+      expect(event.string).toBe newText
+      expect(event.preRange).toEqual expectedPreRange
+      expect(event.postRange).toEqual(new Range([0, 0], [1, 14]))
+
   describe ".save()", ->
     describe "when the buffer has a path", ->
       filePath = null
diff --git a/spec/atom/editor-spec.coffee b/spec/atom/editor-spec.coffee
index 0b345e826..d6e249365 100644
--- a/spec/atom/editor-spec.coffee
+++ b/spec/atom/editor-spec.coffee
@@ -25,6 +25,26 @@ describe "Editor", ->
       expect(buffer.getLine(10)).toBe ''
       expect(editor.lines.find('pre:eq(10)').html()).toBe ' '
 
+    it "syntax highlights code based on the file type", ->
+      line1 = editor.lines.find('.line:first')
+      expect(line1.find('span:eq(0)')).toMatchSelector '.keyword.definition'
+      expect(line1.find('span:eq(0)').text()).toBe 'var'
+      expect(line1.find('span:eq(1)')).toMatchSelector '.text'
+      expect(line1.find('span:eq(1)').text()).toBe ' '
+      expect(line1.find('span:eq(2)')).toMatchSelector '.identifier'
+      expect(line1.find('span:eq(2)').text()).toBe 'quicksort'
+      expect(line1.find('span:eq(4)')).toMatchSelector '.operator'
+      expect(line1.find('span:eq(4)').text()).toBe '='
+
+      line12 = editor.lines.find('.line:eq(11)')
+      expect(line12.find('span:eq(1)')).toMatchSelector '.keyword'
+
+    describe "when lines are updated in the buffer", ->
+      it "syntax highlights the updated lines", ->
+        expect(editor.lines.find('.line:eq(0) span:eq(0)')).toMatchSelector '.keyword.definition'
+        buffer.insert([0, 4], "g")
+        expect(editor.lines.find('.line:eq(0) span:eq(0)')).toMatchSelector '.keyword.definition'
+
   describe "cursor movement", ->
     describe ".setCursorPosition({row, column})", ->
       beforeEach ->
diff --git a/spec/atom/highlighter-spec.coffee b/spec/atom/highlighter-spec.coffee
new file mode 100644
index 000000000..37cdb4d26
--- /dev/null
+++ b/spec/atom/highlighter-spec.coffee
@@ -0,0 +1,69 @@
+Highlighter = require 'highlighter'
+Buffer = require 'buffer'
+Range = require 'range'
+
+describe "Highlighter", ->
+  [highlighter, buffer] = []
+
+  beforeEach ->
+    buffer = new Buffer(require.resolve('fixtures/sample.js'))
+    highlighter = new Highlighter(buffer)
+
+  describe "constructor", ->
+    it "tokenizes all the lines in the buffer", ->
+      expect(highlighter.tokensForRow(0)[0]).toEqual(type: 'keyword.definition', value: 'var')
+      expect(highlighter.tokensForRow(11)[1]).toEqual(type: 'keyword', value: 'return')
+
+  describe "when the buffer changes", ->
+    describe "when lines are updated, but none are added or removed", ->
+      it "updates tokens for each of the changed lines", ->
+        buffer.change(new Range([0, 0], [2, 0]), "foo()\nbar()\n")
+
+        expect(highlighter.tokensForRow(0)[0]).toEqual(type: 'identifier', value: 'foo')
+        expect(highlighter.tokensForRow(1)[0]).toEqual(type: 'identifier', value: 'bar')
+
+        # line 2 is unchanged
+        expect(highlighter.tokensForRow(2)[1]).toEqual(type: 'keyword', value: 'if')
+
+      it "updates tokens for lines beyond the changed lines if needed", ->
+        buffer.insert([5, 30], '/* */')
+        buffer.insert([2, 0], '/*')
+        expect(highlighter.tokensForRow(3)[0].type).toBe 'comment'
+        expect(highlighter.tokensForRow(4)[0].type).toBe 'comment'
+        expect(highlighter.tokensForRow(5)[0].type).toBe 'comment'
+
+    describe "when lines are both updated and removed", ->
+      it "updates tokens to reflect the removed lines", ->
+        buffer.change(new Range([1, 0], [3, 0]), "foo()")
+
+        # previous line 0 remains
+        expect(highlighter.tokensForRow(0)[0]).toEqual(type: 'keyword.definition', value: 'var')
+
+        # previous line 3 should be combined with input to form line 1
+        expect(highlighter.tokensForRow(1)[0]).toEqual(type: 'identifier', value: 'foo')
+        expect(highlighter.tokensForRow(1)[6]).toEqual(type: 'identifier', value: 'pivot')
+
+        # lines below deleted regions should be shifted upward
+        expect(highlighter.tokensForRow(2)[1]).toEqual(type: 'keyword', value: 'while')
+        expect(highlighter.tokensForRow(3)[1]).toEqual(type: 'identifier', value: 'current')
+        expect(highlighter.tokensForRow(4)[3]).toEqual(type: 'keyword.operator', value: '<')
+
+    describe "when lines are both updated and inserted", ->
+      it "updates tokens to reflect the inserted lines", ->
+        buffer.change(new Range([1, 0], [2, 0]), "foo()\nbar()\nbaz()\nquux()")
+
+        # previous line 0 remains
+        expect(highlighter.tokensForRow(0)[0]).toEqual(type: 'keyword.definition', value: 'var')
+
+        # 3 new lines inserted
+        expect(highlighter.tokensForRow(1)[0]).toEqual(type: 'identifier', value: 'foo')
+        expect(highlighter.tokensForRow(2)[0]).toEqual(type: 'identifier', value: 'bar')
+        expect(highlighter.tokensForRow(3)[0]).toEqual(type: 'identifier', value: 'baz')
+
+        # previous line 2 is joined with quux() on line 4
+        expect(highlighter.tokensForRow(4)[0]).toEqual(type: 'identifier', value: 'quux')
+        expect(highlighter.tokensForRow(4)[4]).toEqual(type: 'keyword', value: 'if')
+
+        # previous line 3 is pushed down to become line 5
+        expect(highlighter.tokensForRow(5)[3]).toEqual(type: 'identifier', value: 'pivot')
+
diff --git a/src/atom/buffer.coffee b/src/atom/buffer.coffee
index 5bc3ebcdc..661f82cce 100644
--- a/src/atom/buffer.coffee
+++ b/src/atom/buffer.coffee
@@ -1,4 +1,6 @@
+_ = require 'underscore'
 fs = require 'fs'
+Range = require 'range'
 
 module.exports =
 class Buffer
@@ -6,6 +8,7 @@ class Buffer
 
   constructor: (@path) ->
     @url = @path # we want this to be path on master, but let's not break it on a branch
+    @lines = ['']
     if @path and fs.exists(@path)
       @setText(fs.read(@path))
     else
@@ -15,7 +18,10 @@ class Buffer
     @lines.join('\n')
 
   setText: (text) ->
-    @lines = text.split('\n')
+    @change(@getRange(), text)
+
+  getRange: ->
+    new Range([0, 0], [@lastRow(), @lastLine().length])
 
   getTextInRange: (range) ->
     if range.start.row == range.end.row
@@ -35,46 +41,38 @@ class Buffer
   getLine: (row) ->
     @lines[row]
 
-  change: (preRange, string) ->
-    @remove(preRange)
-    postRange = @insert(preRange.start, string)
-    @trigger 'change', { preRange, postRange, string }
-
-  remove: (range) ->
-    prefix = @lines[range.start.row][0...range.start.column]
-    suffix = @lines[range.end.row][range.end.column..]
-    @lines[range.start.row..range.end.row] = prefix + suffix
-
-  insert: ({row, column}, string) ->
-    postRange =
-      start: { row, column }
-      end: { row, column }
-
-    prefix = @lines[row][0...column]
-    suffix = @lines[row][column..]
-
-    lines = string.split('\n')
-
-    if lines.length == 1
-      @lines[row] = prefix + string + suffix
-      postRange.end.column += string.length
-    else
-      for line, i in lines
-        curRow = row + i
-        if i == 0 # replace first line
-          @lines[curRow] = prefix + line
-        else if i < lines.length - 1 # insert middle lines
-          @lines[curRow...curRow] = line
-        else # insert last line
-          @lines[curRow...curRow] = line + suffix
-          postRange.end.row = curRow
-          postRange.end.column = line.length
-
-    postRange
-
   numLines: ->
     @getLines().length
 
+  lastRow: ->
+    @getLines().length - 1
+
+  lastLine: ->
+    @getLine(@lastRow())
+
+  insert: (point, text) ->
+    @change(new Range(point, point), text)
+
+  change: (preRange, newText) ->
+    postRange = new Range(_.clone(preRange.start), _.clone(preRange.start))
+    prefix = @lines[preRange.start.row][0...preRange.start.column]
+    suffix = @lines[preRange.end.row][preRange.end.column..]
+
+    newTextLines = newText.split('\n')
+
+    if newTextLines.length == 1
+      postRange.end.column += newText.length
+      newTextLines = [prefix + newText + suffix]
+    else
+      lastLineIndex = newTextLines.length - 1
+      newTextLines[0] = prefix + newTextLines[0]
+      postRange.end.row += lastLineIndex
+      postRange.end.column = newTextLines[lastLineIndex].length
+      newTextLines[lastLineIndex] += suffix
+
+    @lines[preRange.start.row..preRange.end.row] = newTextLines
+    @trigger 'change', { preRange, postRange, string: newText }
+
   save: ->
     if not @path then throw new Error("Tried to save buffer with no url")
     fs.write @path, @getText()
@@ -87,3 +85,14 @@ class Buffer
   trigger: (eventName, event) ->
     @eventHandlers?[eventName]?.forEach (handler) -> handler(event)
 
+  modeName: ->
+    extension = if @path then @path.split('/').pop().split('.').pop() else null
+    switch extension
+      when 'js' then 'javascript'
+      when 'coffee' then 'coffee'
+      when 'rb', 'ru' then 'ruby'
+      when 'c', 'h', 'cpp' then 'c_cpp'
+      when 'html', 'htm' then 'html'
+      when 'css' then 'css'
+      else 'text'
+
diff --git a/src/atom/editor.coffee b/src/atom/editor.coffee
index c2f525c4b..cc79268ee 100644
--- a/src/atom/editor.coffee
+++ b/src/atom/editor.coffee
@@ -3,7 +3,9 @@ Buffer = require 'buffer'
 Point = require 'point'
 Cursor = require 'cursor'
 Selection = require 'selection'
+Highlighter = require 'highlighter'
 Range = require 'range'
+
 $ = require 'jquery'
 $$ = require 'template/builder'
 _ = require 'underscore'
@@ -26,6 +28,7 @@ class Editor extends Template
 
     initialize: () ->
       requireStylesheet 'editor.css'
+      requireStylesheet 'theme/twilight.css'
       @bindKeys()
       @buildCursorAndSelection()
       @handleEvents()
@@ -97,16 +100,23 @@ class Editor extends Template
         @hiddenInput.width(@charWidth)
         @focus()
 
-    buildLineElement: (lineText) ->
-      if lineText is ''
-        $$.pre class: "line", -> @raw('&nbsp;')
-      else
-        $$.pre class: "line", lineText
+    buildLineElement: (row) ->
+      tokens = @highlighter.tokensForRow(row)
+      $$.pre class: 'line', ->
+        if tokens.length
+          for token in tokens
+            classes = token.type.split('.').map((c) -> "ace_#{c}").join(' ')
+            @span { class: token.type.replace('.', ' ') }, token.value
+        else
+          @raw '&nbsp;'
 
     setBuffer: (@buffer) ->
+      @highlighter = new Highlighter(@buffer)
+
       @lines.empty()
-      for line in @buffer.getLines()
-        @lines.append @buildLineElement(line)
+      for row in [0..@buffer.lastRow()]
+        line = @buildLineElement(row)
+        @lines.append line
 
       @setCursorPosition(row: 0, column: 0)
 
@@ -128,18 +138,13 @@ class Editor extends Template
             else
               @updateLineElement(row)
 
-        @selection.bufferChanged(e)
+        @cursor.bufferChanged(e)
 
     updateLineElement: (row) ->
-      line = @buffer.getLine(row)
-      element = @getLineElement(row)
-      if line == ''
-        element.html('&nbsp;')
-      else
-        element.text(line)
+      @getLineElement(row).replaceWith(@buildLineElement(row))
 
     insertLineElement: (row) ->
-      @getLineElement(row).before(@buildLineElement(@buffer.getLine(row)))
+      @getLineElement(row).before(@buildLineElement(row))
 
     removeLineElement: (row) ->
       @getLineElement(row).remove()
diff --git a/src/atom/highlighter.coffee b/src/atom/highlighter.coffee
new file mode 100644
index 000000000..33c4a5a74
--- /dev/null
+++ b/src/atom/highlighter.coffee
@@ -0,0 +1,43 @@
+_ = require 'underscore'
+
+module.exports =
+class Highlighter
+  buffer: null
+  tokenizer: null
+  lines: []
+
+  constructor: (@buffer) ->
+    @buildTokenizer()
+    @lines = @tokenizeRows('start', 0, @buffer.lastRow())
+    @buffer.on 'change', (e) => @handleBufferChange(e)
+
+  buildTokenizer: ->
+    Mode = require("ace/mode/#{@buffer.modeName()}").Mode
+    @tokenizer = (new Mode).getTokenizer()
+
+  handleBufferChange: (e) ->
+    { preRange, postRange } = e
+
+    previousState = @lines[preRange.end.row].state
+    newLines = @tokenizeRows('start', postRange.start.row, postRange.end.row)
+    @lines[preRange.start.row..preRange.end.row] = newLines
+
+    for row in [postRange.end.row...@buffer.lastRow()]
+      break if @lines[row].state == previousState
+      nextRow = row + 1
+      previousState = @lines[nextRow].state
+      @lines[nextRow] = @tokenizeRow(@lines[row].state, nextRow)
+
+  tokenizeRows: (startState, startRow, endRow) ->
+    state = startState
+    for row in [startRow..endRow]
+      line = @tokenizeRow(state, row)
+      state = line.state
+      line
+
+  tokenizeRow: (state, row) ->
+    @tokenizer.getLineTokens(@buffer.getLine(row), state)
+
+  tokensForRow: (row) ->
+    @lines[row].tokens
+
diff --git a/src/atom/selection.coffee b/src/atom/selection.coffee
index 9bebfcdf5..52c12c731 100644
--- a/src/atom/selection.coffee
+++ b/src/atom/selection.coffee
@@ -26,9 +26,6 @@ class Selection extends Template
       @anchor = null
       @updateAppearance()
 
-    bufferChanged: (e) ->
-      @cursor.setPosition(e.postRange.end)
-
     updateAppearance: ->
       @clearRegions()
 
diff --git a/static/theme/twilight.css b/static/theme/twilight.css
new file mode 100644
index 000000000..1f782f6b9
--- /dev/null
+++ b/static/theme/twilight.css
@@ -0,0 +1,134 @@
+.editor {
+  border: 2px solid rgb(159, 159, 159);
+}
+
+.editor.focus {
+  border: 2px solid #327fbd;
+}
+
+.gutter {
+  background: #e8e8e8;
+  color: #333;
+}
+
+.print_margin {
+  width: 1px;
+  background: #e8e8e8;
+}
+
+.scroller {
+  background-color: #141414;
+}
+
+.text-layer {
+  cursor: text;
+  color: #F8F8F8;
+}
+
+.cursor {
+  border-left: 2px solid #A7A7A7;
+}
+
+.cursor.overwrite {
+  border-left: 0px;
+  border-bottom: 1px solid #A7A7A7;
+}
+
+.marker-layer .selection {
+  background: rgba(221, 240, 255, 0.20);
+}
+
+.marker-layer .step {
+  background: rgb(198, 219, 174);
+}
+
+.marker-layer .bracket {
+  margin: -1px 0 0 -1px;
+  border: 1px solid rgba(255, 255, 255, 0.25);
+}
+
+.marker-layer .active_line {
+  background: rgba(255, 255, 255, 0.031);
+}
+
+.marker-layer .selected_word {
+  border: 1px solid rgba(221, 240, 255, 0.20);
+}
+
+.invisible {
+  color: rgba(255, 255, 255, 0.25);
+}
+
+.keyword {
+  color:#CDA869;
+}
+
+.constant {
+  color:#CF6A4C;
+}
+
+.invalid.illegal {
+  color:#F8F8F8;
+background-color:rgba(86, 45, 86, 0.75);
+}
+
+.invalid.deprecated {
+  text-decoration:underline;
+font-style:italic;
+color:#D2A8A1;
+}
+
+.support {
+  color:#9B859D;
+}
+
+.fold {
+    background-color: #AC885B;
+    border-color: #F8F8F8;
+}
+
+.support.function {
+  color:#DAD085;
+}
+
+.string {
+  color:#8F9D6A;
+}
+
+.string.regexp {
+  color:#E9C062;
+}
+
+.comment {
+  font-style:italic;
+color:#5F5A60;
+}
+
+.variable {
+  color:#7587A6;
+}
+
+.xml_pe {
+  color:#494949;
+}
+
+.meta.tag {
+  color:#AC885B;
+}
+
+.entity.name.function {
+  color:#AC885B;
+}
+
+.markup.underline {
+    text-decoration:underline;
+}
+
+.markup.heading {
+  color:#CF6A4C;
+}
+
+.markup.list {
+  color:#F9EE98;
+}";
+