diff --git a/TODO b/TODO
index 4c5b1fc..a5aedf6 100644
--- a/TODO
+++ b/TODO
@@ -5,7 +5,6 @@ Todo:
 - Bulk indent/dedent.
 - Search.
 - Search and replace.
-- Overwrite mode.
 - Large pastes.
 
 
@@ -31,6 +30,7 @@ Done:
 - Put it on github.
 - tab key should align code.
 - Right align the left editor.
+- Overwrite mode.
 
 
 Shelved:
diff --git a/diff_edit/editor.py b/diff_edit/editor.py
index c1a393f..86c0ac5 100755
--- a/diff_edit/editor.py
+++ b/diff_edit/editor.py
@@ -194,6 +194,7 @@ class Editor:
         self.last_height = 40
         self.is_editing = True
         self.theme_index = 0
+        self.is_overwriting = False
         self.previous_term_code = None
         self.history = []
 
@@ -341,8 +342,9 @@ class Editor:
     def insert_text(self, text):
         try:
             current_line = self.text_widget[self.cursor_y]
-            new_line = current_line[:self.cursor_x] + text + current_line[self.cursor_x:]
-            self.text_widget[self.cursor_y] = new_line
+            replace_count = len(text) if self.is_overwriting else 0
+            self.text_widget[self.cursor_y] = (current_line[:self.cursor_x] + text
+                                               + current_line[self.cursor_x+replace_count:])
         except IndexError:
             self.text_widget.append(text)
         self.cursor_x += len(text)
@@ -533,6 +535,9 @@ class Editor:
     def undo(self):
         self.text_widget[:], self._cursor_x, self._cursor_y = self.history.pop()
 
+    def toggle_overwrite(self):
+        self.is_overwriting = not self.is_overwriting
+
     def abort_command(self):
         self.mark = None
         self.ring_bell()
@@ -644,7 +649,8 @@ class Editor:
         terminal.CTRL_L: center_cursor, terminal.ALT_SEMICOLON: comment_lines,
         terminal.ALT_c: cycle_syntax_highlighting, terminal.CTRL_X: prefix, terminal.ESC: quit,
         terminal.CTRL_C: ctrl_c, terminal.CTRL_K: delete_line, terminal.TAB: tab_align,
-        terminal.CTRL_UNDERSCORE: undo, terminal.CTRL_Z: undo, terminal.CTRL_G: abort_command}
+        terminal.CTRL_UNDERSCORE: undo, terminal.CTRL_Z: undo, terminal.CTRL_G: abort_command,
+        terminal.INSERT: toggle_overwrite}
 
 
 def main():
diff --git a/setup.py b/setup.py
index de06887..33f931f 100755
--- a/setup.py
+++ b/setup.py
@@ -18,4 +18,4 @@ setup(name="diff-edit",
       entry_points={"console_scripts": ["diff-edit=diff_edit:main"]},
       install_requires=[
           "pygments==2.10.0", "docopt==0.6.2",
-          "fill3 @ git+https://github.com/ahamilton/eris@v2022.01.27#subdirectory=fill3"])
+          "fill3 @ git+https://github.com/ahamilton/eris@v2022.01.28#subdirectory=fill3"])
diff --git a/tests/editor_test.py b/tests/editor_test.py
index b61ca8f..a0ffccb 100755
--- a/tests/editor_test.py
+++ b/tests/editor_test.py
@@ -80,6 +80,15 @@ class EditorTestCase(unittest.TestCase):
         self._assert_editor("a", (1, 0))
         self.editor.insert_text("bc")
         self._assert_editor("abc", (3, 0))
+        # overwrite
+        self.editor.toggle_overwrite()
+        self.editor.cursor_left()
+        self.editor.insert_text("d")
+        self._assert_editor("abd", (3, 0))
+        self.editor.cursor_left()
+        self.editor.cursor_left()
+        self.editor.insert_text("ef")
+        self._assert_editor("aef", (3, 0))
 
     def test_enter(self):
         self._set_editor("ab", (1, 0))