diff --git a/src/textual_paint/paint.py b/src/textual_paint/paint.py
index 3358e8a..62dc2a1 100755
--- a/src/textual_paint/paint.py
+++ b/src/textual_paint/paint.py
@@ -3577,7 +3577,7 @@ Columns: {len(palette) // 2}
                 classes="buttons",
             )
         )
-        window.content.query_one(RadioSet).border_title = _("Flip and Rotate")
+        window.content.query_one(RadioSet).border_title = _("Flip or rotate")
         window.content.query_one("#flip_horizontal", RadioButton).value = True
         self.mount(window)
 
@@ -3616,7 +3616,65 @@ Columns: {len(palette) // 2}
         self.canvas.refresh()
     
     def action_rotate_by_angle(self) -> None:
-        self.message_box(_("Paint"), "Not implemented.", "ok")
+        """Shows a dialog to rotate the image by a given angle."""
+        # TODO: merge with action_flip_rotate dialog
+        self.close_windows("#rotate_by_angle_dialog")
+        def handle_button(button: Button) -> None:
+            if button.has_class("ok"):
+                radio_button = window.content.query_one("#angle", RadioSet).pressed_button
+                assert radio_button is not None, "There should always be a pressed button; one should've been selected initially."
+                assert radio_button.id is not None, "Each radio button should have been given an ID."
+                angle = int(radio_button.id.split("_")[-1])
+                
+                action = Action(_("Rotate by angle"), Region(0, 0, self.image.width, self.image.height))
+                action.is_full_update = True
+                action.update(self.image)
+                self.add_action(action)
+
+                source = AnsiArtDocument(self.image.width, self.image.height)
+                source.copy(self.image)
+
+                if angle != 180:
+                    self.image.resize(self.image.height, self.image.width)
+                
+                for y in range(self.image.height):
+                    for x in range(self.image.width):
+                        if angle == 90:
+                            self.image.ch[y][x] = source.ch[self.image.width - x - 1][y]
+                            self.image.fg[y][x] = source.fg[self.image.width - x - 1][y]
+                            self.image.bg[y][x] = source.bg[self.image.width - x - 1][y]
+                        elif angle == 180:
+                            self.image.ch[y][x] = source.ch[self.image.height - y - 1][self.image.width - x - 1]
+                            self.image.fg[y][x] = source.fg[self.image.height - y - 1][self.image.width - x - 1]
+                            self.image.bg[y][x] = source.bg[self.image.height - y - 1][self.image.width - x - 1]
+                        elif angle == 270:
+                            self.image.ch[y][x] = source.ch[x][self.image.height - y - 1]
+                            self.image.fg[y][x] = source.fg[x][self.image.height - y - 1]
+                            self.image.bg[y][x] = source.bg[x][self.image.height - y - 1]
+                self.canvas.refresh(layout=True)
+            window.close()
+        window = DialogWindow(
+            id="rotate_by_angle_dialog",
+            title=_("Rotate by angle"),
+            handle_button=handle_button,
+        )
+        window.content.mount(
+            RadioSet(
+                RadioButton(_("90°"), id="angle_90"),
+                RadioButton(_("180°"), id="angle_180"),
+                RadioButton(_("270°"), id="angle_270"),
+                classes="autofocus",
+                id="angle",
+            ),
+            Container(
+                Button(_("OK"), classes="ok submit", variant="primary"),
+                Button(_("Cancel"), classes="cancel"),
+                classes="buttons",
+            )
+        )
+        window.content.query_one(RadioSet).border_title = _("Rotate by angle")
+        window.content.query_one("#angle_90", RadioButton).value = True
+        self.mount(window)
 
     def action_stretch_skew(self) -> None:
         self.message_box(_("Paint"), "Not implemented.", "ok")