diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index bdadef5f6e..4d5410f513 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -12,7 +12,7 @@ on:
 
 env:
   min_python_version: "3.8"
-  max_python_version: "3.11"
+  max_python_version: "3.12"
 
 defaults:
   run:
@@ -65,12 +65,12 @@ jobs:
     strategy:
       matrix:
         platform: [ "macos", "ubuntu", "windows" ]
-        python-version: [ "3.8", "3.9", "3.10", "3.11", "3.12-dev" ]
+        python-version: [ "3.8", "3.9", "3.10", "3.11", "3.12" ]
         include:
           - experimental: false
 
-          - python-version: "3.12-dev"
-            experimental: true
+          # - python-version: "3.13-dev"
+          #   experimental: true
     steps:
     - uses: actions/checkout@v4.1.0
     - name: Set up Python ${{ matrix.python-version }}
diff --git a/changes/1215.bugfix.rst b/changes/1215.bugfix.rst
new file mode 100644
index 0000000000..e4bc5ad084
--- /dev/null
+++ b/changes/1215.bugfix.rst
@@ -0,0 +1 @@
+Widgets are now removed from windows when the window is closed, preventing a memory leak on window closure.
diff --git a/core/src/toga/widgets/base.py b/core/src/toga/widgets/base.py
index 5ea49c2226..5d5b0e7bca 100644
--- a/core/src/toga/widgets/base.py
+++ b/core/src/toga/widgets/base.py
@@ -2,6 +2,7 @@
 
 from builtins import id as identifier
 from typing import TYPE_CHECKING, Iterator, NoReturn
+from weakref import WeakValueDictionary
 
 from travertino.node import Node
 
@@ -13,10 +14,12 @@
     from toga.window import Window
 
 
-class WidgetRegistry(dict):
-    # WidgetRegistry is implemented as a subclass of dict, because it provides
-    # a mapping from ID to widget. However, it exposes a set-like API; add()
-    # and update() take instances to be added, and iteration is over values.
+class WidgetRegistry(WeakValueDictionary):
+    # WidgetRegistry is implemented as a subclass of WeakValueDictionary, because it
+    # provides a mapping from ID to widget. However, it exposes a set-like API; add()
+    # and update() take instances to be added, and iteration is over values. The
+    # mapping is weak so the registry doesn't retain a strong reference to the widget,
+    # preventing memory cleanup.
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
@@ -43,6 +46,9 @@ def remove(self, id: str) -> None:
     def __iter__(self) -> Iterator[Widget]:
         return iter(self.values())
 
+    def __repr__(self) -> str:
+        return "{" + ", ".join(f"{k!r}: {v!r}" for k, v in self.items()) + "}"
+
 
 class Widget(Node):
     _MIN_WIDTH = 100
diff --git a/core/src/toga/window.py b/core/src/toga/window.py
index dd236dbd43..f223ee31f5 100644
--- a/core/src/toga/window.py
+++ b/core/src/toga/window.py
@@ -116,6 +116,7 @@ def __init__(
         self._impl = None
         self._content = None
         self._is_full_screen = False
+        self._closed = False
 
         self._resizable = resizable
         self._closable = closable
@@ -155,6 +156,11 @@ def app(self, app: App) -> None:
         self._app = app
         self._impl.set_app(app._impl)
 
+    @property
+    def closed(self) -> bool:
+        """Whether the window was closed."""
+        return self._closed
+
     @property
     def _default_title(self) -> str:
         return "Toga"
@@ -298,9 +304,15 @@ def close(self) -> None:
 
         This *does not* invoke the ``on_close`` handler; the window will be immediately
         and unconditionally closed.
+
+        Once a window has been closed, it *cannot* be reused. The behavior of any method
+        or property on a :class:`~toga.Window` instance after it has been closed is
+        undefined, except for :attr:`closed` which can be used to check if the window
+        was closed.
         """
         self.app.windows -= self
         self._impl.close()
+        self._closed = True
 
     ############################################################
     # Dialogs
diff --git a/core/tests/test_window.py b/core/tests/test_window.py
index 5b67dbebd5..09bbf28ee4 100644
--- a/core/tests/test_window.py
+++ b/core/tests/test_window.py
@@ -253,6 +253,7 @@ def test_close_direct(window, app):
     window.close()
 
     # Window has been closed, but the close handler has *not* been invoked.
+    assert window.closed
     assert window.app == app
     assert window not in app.windows
     assert_action_performed(window, "close")
@@ -269,6 +270,7 @@ def test_close_no_handler(window, app):
     window._impl.simulate_close()
 
     # Window has been closed, and is no longer in the app's list of windows.
+    assert window.closed
     assert window.app == app
     assert window not in app.windows
     assert_action_performed(window, "close")
@@ -287,6 +289,7 @@ def test_close_sucessful_handler(window, app):
     window._impl.simulate_close()
 
     # Window has been closed, and is no longer in the app's list of windows.
+    assert window.closed
     assert window.app == app
     assert window not in app.windows
     assert_action_performed(window, "close")
@@ -306,6 +309,7 @@ def test_close_rejected_handler(window, app):
     window._impl.simulate_close()
 
     # Window has *not* been closed
+    assert not window.closed
     assert window.app == app
     assert window in app.windows
     assert_action_not_performed(window, "close")
diff --git a/core/tests/widgets/test_base.py b/core/tests/widgets/test_base.py
index 3459838236..b3f3ca810a 100644
--- a/core/tests/widgets/test_base.py
+++ b/core/tests/widgets/test_base.py
@@ -123,6 +123,10 @@ def test_add_child(widget):
     assert widget.app == app
     assert widget.window == window
 
+    # Widget is registered with app and window
+    assert widget.id in app.widgets
+    assert widget.id in window.widgets
+
     # Child list is empty
     assert widget.children == []
 
@@ -181,10 +185,7 @@ def test_add_multiple_children(widget):
     child3 = ExampleLeafWidget(id="child3_id")
 
     # App's widget index only contains the parent
-    assert app.widgets["widget_id"] == widget
-    assert "child1_id" not in app.widgets
-    assert "child2_id" not in app.widgets
-    assert "child3_id" not in app.widgets
+    assert app.widgets == {"widget_id": widget}
 
     # Add the children.
     widget.add(child1, child2, child3)
@@ -218,11 +219,20 @@ def test_add_multiple_children(widget):
     assert_action_performed_with(window.content, "refresh")
 
     # App's widget index has been updated
-    assert len(app.widgets) == 4
-    assert app.widgets["widget_id"] == widget
-    assert app.widgets["child1_id"] == child1
-    assert app.widgets["child2_id"] == child2
-    assert app.widgets["child3_id"] == child3
+    assert app.widgets == {
+        "widget_id": widget,
+        "child1_id": child1,
+        "child2_id": child2,
+        "child3_id": child3,
+    }
+
+    # Window's widget index has been updated
+    assert window.widgets == {
+        "widget_id": widget,
+        "child1_id": child1,
+        "child2_id": child2,
+        "child3_id": child3,
+    }
 
 
 def test_reparent_child(widget):
@@ -375,9 +385,16 @@ def test_insert_child(widget):
     assert_action_performed_with(window.content, "refresh")
 
     # App's widget index has been updated
-    assert len(app.widgets) == 2
-    assert app.widgets["widget_id"] == widget
-    assert app.widgets["child_id"] == child
+    assert app.widgets == {
+        "widget_id": widget,
+        "child_id": child,
+    }
+
+    # Window's widget index has been updated
+    assert window.widgets == {
+        "widget_id": widget,
+        "child_id": child,
+    }
 
 
 def test_insert_position(widget):
@@ -402,10 +419,10 @@ def test_insert_position(widget):
     child3 = ExampleLeafWidget(id="child3_id")
 
     # App's widget index only contains the parent
-    assert app.widgets["widget_id"] == widget
-    assert "child1_id" not in app.widgets
-    assert "child2_id" not in app.widgets
-    assert "child3_id" not in app.widgets
+    assert app.widgets == {"widget_id": widget}
+
+    # Windows's widget index only contains the parent
+    assert window.widgets == {"widget_id": widget}
 
     # insert the children.
     widget.insert(0, child1)
@@ -440,11 +457,20 @@ def test_insert_position(widget):
     assert_action_performed_with(window.content, "refresh")
 
     # App's widget index has been updated
-    assert len(app.widgets) == 4
-    assert app.widgets["widget_id"] == widget
-    assert app.widgets["child1_id"] == child1
-    assert app.widgets["child2_id"] == child2
-    assert app.widgets["child3_id"] == child3
+    assert app.widgets == {
+        "widget_id": widget,
+        "child1_id": child1,
+        "child2_id": child2,
+        "child3_id": child3,
+    }
+
+    # Window's widget index has been updated
+    assert window.widgets == {
+        "widget_id": widget,
+        "child1_id": child1,
+        "child2_id": child2,
+        "child3_id": child3,
+    }
 
 
 def test_insert_bad_position(widget):
@@ -467,10 +493,12 @@ def test_insert_bad_position(widget):
     child = ExampleLeafWidget(id="child_id")
 
     # App's widget index only contains the parent
-    assert app.widgets["widget_id"] == widget
-    assert "child_id" not in app.widgets
+    assert app.widgets == {"widget_id": widget}
+
+    # Window's widget index only contains the parent
+    assert window.widgets == {"widget_id": widget}
 
-    # Insert the child at an position greater than the length of the list.
+    # Insert the child at a position greater than the length of the list.
     # Widget will be added to the end of the list.
     widget.insert(37, child)
 
@@ -492,9 +520,16 @@ def test_insert_bad_position(widget):
     assert_action_performed_with(window.content, "refresh")
 
     # App's widget index has been updated
-    assert len(app.widgets) == 2
-    assert app.widgets["widget_id"] == widget
-    assert app.widgets["child_id"] == child
+    assert app.widgets == {
+        "widget_id": widget,
+        "child_id": child,
+    }
+
+    # Window's widget index has been updated
+    assert window.widgets == {
+        "widget_id": widget,
+        "child_id": child,
+    }
 
 
 def test_insert_reparent_child(widget):
@@ -618,6 +653,8 @@ def test_remove_child(widget):
     assert child.parent == widget
     assert child.app == app
     assert child.window == window
+    assert app.widgets == {"widget_id": widget, "child_id": child}
+    assert window.widgets == {"widget_id": widget, "child_id": child}
 
     # Remove the child
     widget.remove(child)
@@ -630,6 +667,10 @@ def test_remove_child(widget):
     assert child.app is None
     assert child.window is None
 
+    # child widget no longer exists in the app or widgets registries.
+    assert app.widgets == {"widget_id": widget}
+    assert window.widgets == {"widget_id": widget}
+
     # The impl's remove_child has been invoked
     assert_action_performed_with(widget, "remove child", child=child._impl)
 
@@ -639,6 +680,9 @@ def test_remove_child(widget):
     # The window's content gets a refresh notification
     assert_action_performed_with(window.content, "refresh")
 
+    # App's widget index does not contain the widget
+    assert "child_id" not in app.widgets
+
 
 def test_remove_multiple_children(widget):
     "Multiple children can be removed from a widget"
@@ -659,6 +703,8 @@ def test_remove_multiple_children(widget):
         assert child.parent == widget
         assert child.app == app
         assert child.window == window
+        assert app.widgets[child.id] == child
+        assert window.widgets[child.id] == child
 
     # Remove 2 children
     widget.remove(child1, child3)
@@ -689,6 +735,14 @@ def test_remove_multiple_children(widget):
     # The window's content gets a refresh notification
     assert_action_performed_with(window.content, "refresh")
 
+    # App's widget index does not contain the widget
+    assert "child1_id" not in app.widgets
+    assert "child3_id" not in app.widgets
+
+    # Windows's widget index does not contain the widget
+    assert "child1_id" not in window.widgets
+    assert "child3_id" not in window.widgets
+
 
 def test_clear_all_children(widget):
     "All children can be simultaneously removed from a widget"
@@ -709,6 +763,8 @@ def test_clear_all_children(widget):
         assert child.parent == widget
         assert child.app == app
         assert child.window == window
+        assert app.widgets[child.id] == child
+        assert window.widgets[child.id] == child
 
     # Clear children
     widget.clear()
@@ -740,6 +796,16 @@ def test_clear_all_children(widget):
     # The window's content gets a refresh notification
     assert_action_performed_with(window.content, "refresh")
 
+    # App's widget index does not contain the widget
+    assert "child1_id" not in app.widgets
+    assert "child2_id" not in app.widgets
+    assert "child3_id" not in app.widgets
+
+    # Window's widget index does not contain the widget
+    assert "child1_id" not in window.widgets
+    assert "child2_id" not in window.widgets
+    assert "child3_id" not in window.widgets
+
 
 def test_clear_no_children(widget):
     "No changes are made (no-op) if widget has no children"
@@ -830,7 +896,7 @@ def test_set_app(widget):
     assert len(app.widgets) == 1
     assert app.widgets["widget_id"] == widget
 
-    # The impl has had it's app property set.
+    # The impl has had its app property set.
     assert attribute_value(widget, "app") == app
 
 
diff --git a/docs/reference/api/window.rst b/docs/reference/api/window.rst
index 50e0b94f79..f622a9cd5f 100644
--- a/docs/reference/api/window.rst
+++ b/docs/reference/api/window.rst
@@ -46,6 +46,10 @@ If the user attempts to close the window, Toga will call the ``on_close`` handle
 handler must return a ``bool`` confirming whether the close is permitted. This can be
 used to implement protections against closing a window with unsaved changes.
 
+Once a window has been closed (either by user action, or programmatically with
+:meth:`~toga.Window.close()`), it *cannot* be reused. The behavior of any method on a
+:class:`~toga.Window` instance after it has been closed is undefined.
+
 Notes
 -----
 
diff --git a/testbed/tests/test_window.py b/testbed/tests/test_window.py
index 59607fed7b..11acca0453 100644
--- a/testbed/tests/test_window.py
+++ b/testbed/tests/test_window.py
@@ -1,6 +1,8 @@
+import gc
 import io
 import re
 import traceback
+import weakref
 from asyncio import wait_for
 from importlib import import_module
 from pathlib import Path
@@ -219,6 +221,32 @@ async def test_secondary_window_with_args(app, second_window, second_window_prob
 
         assert second_window not in app.windows
 
+    async def test_secondary_window_cleanup(app_probe):
+        """Memory for windows is cleaned up when windows are deleted."""
+        # Create and show a window with content. We can't use the second_window fixture
+        # because the fixture will retain a reference, preventing garbage collection.
+        second_window = toga.Window()
+        second_window.content = toga.Box()
+        second_window.show()
+        await app_probe.redraw("Secondary Window has been created")
+
+        # Retain a weak reference to the window to check garbage collection
+        window_ref = weakref.ref(second_window)
+        impl_ref = weakref.ref(second_window._impl)
+
+        second_window.close()
+        await app_probe.redraw("Secondary window has been closed")
+
+        # Clear the local reference to the window (which should be the last reference),
+        # and force a garbage collection pass. This should cause deletion of both the
+        # interface and impl of the window.
+        del second_window
+        gc.collect()
+
+        # Assert that the weak references are now dead.
+        assert window_ref() is None
+        assert impl_ref() is None
+
     @pytest.mark.parametrize(
         "second_window_kwargs",
         [dict(title="Not Resizable", resizable=False, position=(200, 150))],
diff --git a/testbed/tests/widgets/test_webview.py b/testbed/tests/widgets/test_webview.py
index f6b28f1a03..10dcb6dd18 100644
--- a/testbed/tests/widgets/test_webview.py
+++ b/testbed/tests/widgets/test_webview.py
@@ -1,4 +1,5 @@
 import asyncio
+import gc
 from asyncio import wait_for
 from contextlib import nullcontext
 from time import time
@@ -78,6 +79,13 @@ async def on_load():
 
 @pytest.fixture
 async def widget(on_load):
+    if toga.platform.current_platform == "linux":
+        # On Gtk, ensure that the WebView from a previous test run is garbage collected.
+        # This prevents a segfault at GC time likely coming from the test suite running
+        # in a thread and Gtk WebViews sharing resources between instances. We perform
+        # the GC run here since pytest fixtures make earlier cleanup difficult.
+        gc.collect()
+
     widget = toga.WebView(style=Pack(flex=1), on_webview_load=on_load)
     # We shouldn't be able to get a callback until at least one tick of the event loop
     # has completed.
diff --git a/winforms/src/toga_winforms/app.py b/winforms/src/toga_winforms/app.py
index 7633a37611..3e1e4d9aab 100644
--- a/winforms/src/toga_winforms/app.py
+++ b/winforms/src/toga_winforms/app.py
@@ -15,6 +15,7 @@
 
 from .keys import toga_to_winforms_key
 from .libs.proactor import WinformsProactorEventLoop
+from .libs.wrapper import WeakrefCallable
 from .window import Window
 
 
@@ -154,7 +155,7 @@ def create_menus(self):
                 item = WinForms.ToolStripMenuItem(cmd.text)
 
                 if cmd.action:
-                    item.Click += cmd._impl.as_handler()
+                    item.Click += WeakrefCallable(cmd._impl.as_handler())
                 item.Enabled = cmd.enabled
 
                 if cmd.shortcut is not None:
@@ -247,7 +248,9 @@ def run_app(self):
 
             # This catches errors in handlers, and prints them
             # in a usable form.
-            self.native.ThreadException += self.winforms_thread_exception
+            self.native.ThreadException += WeakrefCallable(
+                self.winforms_thread_exception
+            )
 
             self.loop.run_forever(self)
         except Exception as e:
diff --git a/winforms/src/toga_winforms/dialogs.py b/winforms/src/toga_winforms/dialogs.py
index 2c8cfad9e0..5b82d9e5ca 100644
--- a/winforms/src/toga_winforms/dialogs.py
+++ b/winforms/src/toga_winforms/dialogs.py
@@ -12,6 +12,8 @@
 )
 from System.Windows.Forms import DialogResult, MessageBoxButtons, MessageBoxIcon
 
+from .libs.wrapper import WeakrefCallable
+
 
 class BaseDialog(ABC):
     def __init__(self, interface, on_result):
@@ -102,7 +104,7 @@ def __init__(self, interface, title, message, content, retry, on_result):
         self.native.MinimizeBox = False
         self.native.FormBorderStyle = self.native.FormBorderStyle.FixedSingle
         self.native.MaximizeBox = False
-        self.native.FormClosing += self.winforms_FormClosing
+        self.native.FormClosing += WeakrefCallable(self.winforms_FormClosing)
         self.native.Width = 540
         self.native.Height = 320
         self.native.Text = title
@@ -141,7 +143,7 @@ def __init__(self, interface, title, message, content, retry, on_result):
             retry.Top = 250
             retry.Width = 100
             retry.Text = "&Retry"
-            retry.Click += self.winforms_Click_retry
+            retry.Click += WeakrefCallable(self.winforms_Click_retry)
 
             self.native.Controls.Add(retry)
 
@@ -150,7 +152,7 @@ def __init__(self, interface, title, message, content, retry, on_result):
             quit.Top = 250
             quit.Width = 100
             quit.Text = "&Quit"
-            quit.Click += self.winforms_Click_quit
+            quit.Click += WeakrefCallable(self.winforms_Click_quit)
 
             self.native.Controls.Add(quit)
         else:
@@ -159,7 +161,7 @@ def __init__(self, interface, title, message, content, retry, on_result):
             accept.Top = 250
             accept.Width = 100
             accept.Text = "&OK"
-            accept.Click += self.winforms_Click_accept
+            accept.Click += WeakrefCallable(self.winforms_Click_accept)
 
             self.native.Controls.Add(accept)
 
diff --git a/winforms/src/toga_winforms/libs/wrapper.py b/winforms/src/toga_winforms/libs/wrapper.py
new file mode 100644
index 0000000000..958db4cc66
--- /dev/null
+++ b/winforms/src/toga_winforms/libs/wrapper.py
@@ -0,0 +1,22 @@
+import weakref
+
+
+class WeakrefCallable:
+    """
+    A wrapper for callable that holds a weak reference to it.
+
+    This can be useful in particular when setting winforms event handlers, to avoid
+    cyclical reference cycles between Python and the .NET CLR that are detected neither
+    by the Python garbage collector nor the C# garbage collector.
+    """
+
+    def __init__(self, function):
+        try:
+            self.ref = weakref.WeakMethod(function)
+        except TypeError:
+            self.ref = weakref.ref(function)
+
+    def __call__(self, *args, **kwargs):
+        function = self.ref()
+        if function:
+            return function(*args, **kwargs)
diff --git a/winforms/src/toga_winforms/widgets/box.py b/winforms/src/toga_winforms/widgets/box.py
index 82c00a41fc..6025c443a8 100644
--- a/winforms/src/toga_winforms/widgets/box.py
+++ b/winforms/src/toga_winforms/widgets/box.py
@@ -7,7 +7,6 @@
 class Box(Widget):
     def create(self):
         self.native = WinForms.Panel()
-        self.native.interface = self.interface
 
     def rehint(self):
         self.interface.intrinsic.width = at_least(0)
diff --git a/winforms/src/toga_winforms/widgets/button.py b/winforms/src/toga_winforms/widgets/button.py
index caf699f35d..372a2c06b5 100644
--- a/winforms/src/toga_winforms/widgets/button.py
+++ b/winforms/src/toga_winforms/widgets/button.py
@@ -1,6 +1,7 @@
 import System.Windows.Forms as WinForms
 from travertino.size import at_least
 
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
@@ -10,7 +11,7 @@ class Button(Widget):
     def create(self):
         self.native = WinForms.Button()
         self.native.AutoSizeMode = WinForms.AutoSizeMode.GrowAndShrink
-        self.native.Click += self.winforms_click
+        self.native.Click += WeakrefCallable(self.winforms_click)
 
     def winforms_click(self, sender, event):
         self.interface.on_press(None)
diff --git a/winforms/src/toga_winforms/widgets/canvas.py b/winforms/src/toga_winforms/widgets/canvas.py
index e762e51658..1d8d6ba8ab 100644
--- a/winforms/src/toga_winforms/widgets/canvas.py
+++ b/winforms/src/toga_winforms/widgets/canvas.py
@@ -24,6 +24,7 @@
 from toga.widgets.canvas import Baseline, FillRule
 from toga_winforms.colors import native_color
 
+from ..libs.wrapper import WeakrefCallable
 from .box import Box
 
 
@@ -71,11 +72,11 @@ class Canvas(Box):
     def create(self):
         super().create()
         self.native.DoubleBuffered = True
-        self.native.Paint += self.winforms_paint
-        self.native.Resize += self.winforms_resize
-        self.native.MouseDown += self.winforms_mouse_down
-        self.native.MouseMove += self.winforms_mouse_move
-        self.native.MouseUp += self.winforms_mouse_up
+        self.native.Paint += WeakrefCallable(self.winforms_paint)
+        self.native.Resize += WeakrefCallable(self.winforms_resize)
+        self.native.MouseDown += WeakrefCallable(self.winforms_mouse_down)
+        self.native.MouseMove += WeakrefCallable(self.winforms_mouse_move)
+        self.native.MouseUp += WeakrefCallable(self.winforms_mouse_up)
         self.string_format = StringFormat.GenericTypographic
         self.dragging = False
         self.states = []
diff --git a/winforms/src/toga_winforms/widgets/dateinput.py b/winforms/src/toga_winforms/widgets/dateinput.py
index 86f8d33c56..adb5077d00 100644
--- a/winforms/src/toga_winforms/widgets/dateinput.py
+++ b/winforms/src/toga_winforms/widgets/dateinput.py
@@ -4,6 +4,7 @@
 from System import DateTime as WinDateTime
 from travertino.size import at_least
 
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
@@ -20,7 +21,7 @@ class DateInput(Widget):
 
     def create(self):
         self.native = WinForms.DateTimePicker()
-        self.native.ValueChanged += self.winforms_value_changed
+        self.native.ValueChanged += WeakrefCallable(self.winforms_value_changed)
 
     def get_value(self):
         return py_date(self.native.Value)
diff --git a/winforms/src/toga_winforms/widgets/detailedlist.py b/winforms/src/toga_winforms/widgets/detailedlist.py
index 58b96f2517..e93d8d70db 100644
--- a/winforms/src/toga_winforms/widgets/detailedlist.py
+++ b/winforms/src/toga_winforms/widgets/detailedlist.py
@@ -41,8 +41,9 @@ def create(self):
         super().create()
         self._table_source = TableSource(self.interface)
 
-        # DetailedList doesn't have an on_activate handler.
-        self.native.MouseDoubleClick -= self.winforms_double_click
+    def add_action_events(self):
+        # DetailedList doesn't have an on_activate_handler.
+        pass
 
     def set_primary_action_enabled(self, enabled):
         self.primary_action_enabled = enabled
diff --git a/winforms/src/toga_winforms/widgets/imageview.py b/winforms/src/toga_winforms/widgets/imageview.py
index d9e9c81a3d..4795c1daf4 100644
--- a/winforms/src/toga_winforms/widgets/imageview.py
+++ b/winforms/src/toga_winforms/widgets/imageview.py
@@ -9,7 +9,6 @@
 class ImageView(Widget):
     def create(self):
         self.native = WinForms.PictureBox()
-        self.native.interface = self.interface
         self.native.SizeMode = WinForms.PictureBoxSizeMode.Zoom
 
         # If self.native.Image is None, Winforms renders it as a white square
diff --git a/winforms/src/toga_winforms/widgets/multilinetextinput.py b/winforms/src/toga_winforms/widgets/multilinetextinput.py
index 41f5c3da16..681e99a2ac 100644
--- a/winforms/src/toga_winforms/widgets/multilinetextinput.py
+++ b/winforms/src/toga_winforms/widgets/multilinetextinput.py
@@ -5,6 +5,7 @@
 from toga_winforms.colors import native_color
 from toga_winforms.libs.fonts import HorizontalTextAlignment
 
+from ..libs.wrapper import WeakrefCallable
 from .textinput import TextInput
 
 
@@ -14,12 +15,12 @@ def create(self):
         # (https://stackoverflow.com/a/612234).
         self.native = WinForms.RichTextBox()
         self.native.Multiline = True
-        self.native.TextChanged += self.winforms_text_changed
+        self.native.TextChanged += WeakrefCallable(self.winforms_text_changed)
 
         # When moving focus with the tab key, the Enter/Leave event handlers see the
         # wrong value of ContainsFocus, so we use GotFocus/LostFocus instead.
-        self.native.GotFocus += self.winforms_got_focus
-        self.native.LostFocus += self.winforms_lost_focus
+        self.native.GotFocus += WeakrefCallable(self.winforms_got_focus)
+        self.native.LostFocus += WeakrefCallable(self.winforms_lost_focus)
 
         # Dummy values used during initialization
         self._placeholder = ""
diff --git a/winforms/src/toga_winforms/widgets/numberinput.py b/winforms/src/toga_winforms/widgets/numberinput.py
index 4639b0480a..9b677d2d60 100644
--- a/winforms/src/toga_winforms/widgets/numberinput.py
+++ b/winforms/src/toga_winforms/widgets/numberinput.py
@@ -8,6 +8,7 @@
 from toga.widgets.numberinput import _clean_decimal
 from toga_winforms.libs.fonts import HorizontalTextAlignment
 
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
@@ -26,7 +27,7 @@ class NumberInput(Widget):
 
     def create(self):
         self.native = WinForms.NumericUpDown()
-        self.native.TextChanged += self.winforms_text_changed
+        self.native.TextChanged += WeakrefCallable(self.winforms_text_changed)
 
     def winforms_text_changed(self, sender, event):
         self.interface.on_change(None)
diff --git a/winforms/src/toga_winforms/widgets/optioncontainer.py b/winforms/src/toga_winforms/widgets/optioncontainer.py
index 1a5ed7ff8e..15bc0e5813 100644
--- a/winforms/src/toga_winforms/widgets/optioncontainer.py
+++ b/winforms/src/toga_winforms/widgets/optioncontainer.py
@@ -2,13 +2,14 @@
 from travertino.size import at_least
 
 from ..container import Container
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
 class OptionContainer(Widget):
     def create(self):
         self.native = TabControl()
-        self.native.Selected += self.winforms_selected
+        self.native.Selected += WeakrefCallable(self.winforms_selected)
         self.panels = []
 
     def add_content(self, index, text, widget):
@@ -24,7 +25,8 @@ def add_content(self, index, text, widget):
         # newly-selected tab's ClientSize is not updated until some time after the
         # Selected event fires.
         self.resize_content(panel)
-        page.ClientSizeChanged += lambda sender, event: self.resize_content(panel)
+
+        page.ClientSizeChanged += WeakrefCallable(self.winforms_client_size_changed)
 
     def remove_content(self, index):
         panel = self.panels.pop(index)
@@ -58,6 +60,10 @@ def set_current_tab_index(self, current_tab_index):
     def winforms_selected(self, sender, event):
         self.interface.on_select(None)
 
+    def winforms_client_size_changed(self, sender, event):
+        for panel in self.panels:
+            self.resize_content(panel)
+
     def resize_content(self, panel):
         size = panel.native_parent.ClientSize
         panel.resize_content(size.Width, size.Height)
diff --git a/winforms/src/toga_winforms/widgets/scrollcontainer.py b/winforms/src/toga_winforms/widgets/scrollcontainer.py
index 2fa3b45ffa..fc7c88b61a 100644
--- a/winforms/src/toga_winforms/widgets/scrollcontainer.py
+++ b/winforms/src/toga_winforms/widgets/scrollcontainer.py
@@ -7,6 +7,7 @@
 
 from toga_winforms.container import Container
 
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 # On Windows, scroll bars usually appear only when the content is larger than the
@@ -36,8 +37,8 @@ def create(self):
         # The Scroll event only fires on direct interaction with the scroll bar. It
         # doesn't fire when using the mouse wheel, and it doesn't fire when setting
         # AutoScrollPosition either, despite the documentation saying otherwise.
-        self.native.Scroll += self.winforms_scroll
-        self.native.MouseWheel += self.winforms_scroll
+        self.native.Scroll += WeakrefCallable(self.winforms_scroll)
+        self.native.MouseWheel += WeakrefCallable(self.winforms_scroll)
 
     def winforms_scroll(self, sender, event):
         self.interface.on_scroll(None)
diff --git a/winforms/src/toga_winforms/widgets/selection.py b/winforms/src/toga_winforms/widgets/selection.py
index bcbfa0d73f..76453965eb 100644
--- a/winforms/src/toga_winforms/widgets/selection.py
+++ b/winforms/src/toga_winforms/widgets/selection.py
@@ -3,6 +3,7 @@
 import System.Windows.Forms as WinForms
 from travertino.size import at_least
 
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
@@ -11,7 +12,9 @@ def __init__(self, impl):
         super().__init__()
         self.impl = impl
         self.DropDownStyle = WinForms.ComboBoxStyle.DropDownList
-        self.SelectedIndexChanged += self.winforms_selected_index_changed
+        self.SelectedIndexChanged += WeakrefCallable(
+            self.winforms_selected_index_changed
+        )
 
     def winforms_selected_index_changed(self, sender, event):
         self.impl.on_change()
diff --git a/winforms/src/toga_winforms/widgets/slider.py b/winforms/src/toga_winforms/widgets/slider.py
index 2ba97d4261..0d5c0cd547 100644
--- a/winforms/src/toga_winforms/widgets/slider.py
+++ b/winforms/src/toga_winforms/widgets/slider.py
@@ -3,6 +3,7 @@
 
 from toga.widgets.slider import IntSliderImpl
 
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 # Implementation notes
@@ -25,9 +26,18 @@ def create(self):
 
         # Unlike Scroll, ValueChanged also fires when the value is changed
         # programmatically, such as via the testbed probe.
-        self.native.ValueChanged += lambda sender, event: self.on_change()
-        self.native.MouseDown += lambda sender, event: self.interface.on_press(None)
-        self.native.MouseUp += lambda sender, event: self.interface.on_release(None)
+        self.native.ValueChanged += WeakrefCallable(self.winforms_value_chaned)
+        self.native.MouseDown += WeakrefCallable(self.winforms_mouse_down)
+        self.native.MouseUp += WeakrefCallable(self.winforms_mouse_up)
+
+    def winforms_value_chaned(self, sender, event):
+        self.on_change()
+
+    def winforms_mouse_down(self, sender, event):
+        self.interface.on_press(None)
+
+    def winforms_mouse_up(self, sender, event):
+        self.interface.on_release(None)
 
     def get_int_value(self):
         return self.native.Value
diff --git a/winforms/src/toga_winforms/widgets/splitcontainer.py b/winforms/src/toga_winforms/widgets/splitcontainer.py
index 0a51ae01c4..f2605fd539 100644
--- a/winforms/src/toga_winforms/widgets/splitcontainer.py
+++ b/winforms/src/toga_winforms/widgets/splitcontainer.py
@@ -8,13 +8,14 @@
 from toga.constants import Direction
 
 from ..container import Container
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
 class SplitContainer(Widget):
     def create(self):
         self.native = NativeSplitContainer()
-        self.native.SplitterMoved += lambda sender, event: self.resize_content()
+        self.native.SplitterMoved += WeakrefCallable(self.winforms_splitter_moved)
 
         # Despite what the BorderStyle documentation says, there is no border by default
         # (at least on Windows 10), which would make the split bar invisible.
@@ -23,6 +24,9 @@ def create(self):
         self.panels = (Container(self.native.Panel1), Container(self.native.Panel2))
         self.pending_position = None
 
+    def winforms_splitter_moved(self, sender, event):
+        self.resize_content()
+
     def set_bounds(self, x, y, width, height):
         super().set_bounds(x, y, width, height)
 
diff --git a/winforms/src/toga_winforms/widgets/switch.py b/winforms/src/toga_winforms/widgets/switch.py
index 09412b51e5..33f6702d62 100644
--- a/winforms/src/toga_winforms/widgets/switch.py
+++ b/winforms/src/toga_winforms/widgets/switch.py
@@ -1,13 +1,14 @@
 import System.Windows.Forms as WinForms
 from travertino.size import at_least
 
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
 class Switch(Widget):
     def create(self):
         self.native = WinForms.CheckBox()
-        self.native.CheckedChanged += self.winforms_checked_changed
+        self.native.CheckedChanged += WeakrefCallable(self.winforms_checked_changed)
 
     def winforms_checked_changed(self, sender, event):
         self.interface.on_change(None)
diff --git a/winforms/src/toga_winforms/widgets/table.py b/winforms/src/toga_winforms/widgets/table.py
index 9e0a0bfe5d..5b8c1a9b43 100644
--- a/winforms/src/toga_winforms/widgets/table.py
+++ b/winforms/src/toga_winforms/widgets/table.py
@@ -5,6 +5,7 @@
 
 import toga
 
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
@@ -54,13 +55,22 @@ def create(self):
         self.native.Columns.AddRange(dataColumn)
         self.native.SmallImageList = WinForms.ImageList()
 
-        self.native.ItemSelectionChanged += self.winforms_item_selection_changed
-        self.native.RetrieveVirtualItem += self.winforms_retrieve_virtual_item
-        self.native.CacheVirtualItems += self.winforms_cache_virtual_items
-        self.native.MouseDoubleClick += self.winforms_double_click
-        self.native.VirtualItemsSelectionRangeChanged += (
+        self.native.ItemSelectionChanged += WeakrefCallable(
             self.winforms_item_selection_changed
         )
+        self.native.RetrieveVirtualItem += WeakrefCallable(
+            self.winforms_retrieve_virtual_item
+        )
+        self.native.CacheVirtualItems += WeakrefCallable(
+            self.winforms_cache_virtual_items
+        )
+        self.native.VirtualItemsSelectionRangeChanged += WeakrefCallable(
+            self.winforms_item_selection_changed
+        )
+        self.add_action_events()
+
+    def add_action_events(self):
+        self.native.MouseDoubleClick += WeakrefCallable(self.winforms_double_click)
 
     def set_bounds(self, x, y, width, height):
         super().set_bounds(x, y, width, height)
diff --git a/winforms/src/toga_winforms/widgets/textinput.py b/winforms/src/toga_winforms/widgets/textinput.py
index b3650872de..08ea69b593 100644
--- a/winforms/src/toga_winforms/widgets/textinput.py
+++ b/winforms/src/toga_winforms/widgets/textinput.py
@@ -7,6 +7,7 @@
 from toga_winforms.colors import native_color
 from toga_winforms.libs.fonts import HorizontalTextAlignment
 
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
@@ -16,10 +17,10 @@ class TextInput(Widget):
     def create(self):
         self.native = WinForms.TextBox()
         self.native.Multiline = False
-        self.native.TextChanged += self.winforms_text_changed
-        self.native.KeyPress += self.winforms_key_press
-        self.native.GotFocus += self.winforms_got_focus
-        self.native.LostFocus += self.winforms_lost_focus
+        self.native.TextChanged += WeakrefCallable(self.winforms_text_changed)
+        self.native.KeyPress += WeakrefCallable(self.winforms_key_press)
+        self.native.GotFocus += WeakrefCallable(self.winforms_got_focus)
+        self.native.LostFocus += WeakrefCallable(self.winforms_lost_focus)
 
         self._placeholder = ""
 
diff --git a/winforms/src/toga_winforms/widgets/timeinput.py b/winforms/src/toga_winforms/widgets/timeinput.py
index 3ee88e121d..eb28fb3d58 100644
--- a/winforms/src/toga_winforms/widgets/timeinput.py
+++ b/winforms/src/toga_winforms/widgets/timeinput.py
@@ -4,6 +4,7 @@
 from System import DateTime as WinDateTime
 from travertino.size import at_least
 
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
@@ -22,7 +23,7 @@ class TimeInput(Widget):
 
     def create(self):
         self.native = WinForms.DateTimePicker()
-        self.native.ValueChanged += self.winforms_value_changed
+        self.native.ValueChanged += WeakrefCallable(self.winforms_value_changed)
         self.native.Format = WinForms.DateTimePickerFormat.Time
         self.native.ShowUpDown = True
 
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index 925fe72e1d..9f38f225a5 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -19,6 +19,7 @@
     WebView2RuntimeNotFoundException,
 )
 
+from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
@@ -35,10 +36,12 @@ def task():
 class WebView(Widget):
     def create(self):
         self.native = WebView2()
-        self.native.CoreWebView2InitializationCompleted += (
+        self.native.CoreWebView2InitializationCompleted += WeakrefCallable(
             self.winforms_initialization_completed
         )
-        self.native.NavigationCompleted += self.winforms_navigation_completed
+        self.native.NavigationCompleted += WeakrefCallable(
+            self.winforms_navigation_completed
+        )
         self.loaded_future = None
 
         props = CoreWebView2CreationProperties()
diff --git a/winforms/src/toga_winforms/window.py b/winforms/src/toga_winforms/window.py
index 0bf021cace..f477d2c924 100644
--- a/winforms/src/toga_winforms/window.py
+++ b/winforms/src/toga_winforms/window.py
@@ -4,13 +4,13 @@
 from toga import GROUP_BREAK, SECTION_BREAK
 
 from .container import Container
+from .libs.wrapper import WeakrefCallable
 from .widgets.base import Scalable
 
 
 class Window(Container, Scalable):
     def __init__(self, interface, title, position, size):
         self.interface = interface
-        self.interface._impl = self
 
         # Winforms close handling is caught on the FormClosing handler. To allow
         # for async close handling, we need to be able to abort this close event,
@@ -20,7 +20,7 @@ def __init__(self, interface, title, position, size):
         self._is_closing = False
 
         self.native = WinForms.Form()
-        self.native.FormClosing += self.winforms_FormClosing
+        self.native.FormClosing += WeakrefCallable(self.winforms_FormClosing)
         super().__init__(self.native)
         self.init_scale(self.native)
 
@@ -32,9 +32,8 @@ def __init__(self, interface, title, position, size):
         self.set_position(position)
 
         self.toolbar_native = None
-        self.toolbar_items = None
 
-        self.native.Resize += lambda sender, args: self.resize_content()
+        self.native.Resize += WeakrefCallable(self.winforms_Resize)
         self.resize_content()  # Store initial size
 
         self.set_full_screen(self.interface.full_screen)
@@ -122,6 +121,9 @@ def hide(self):
     def get_visible(self):
         return self.native.Visible
 
+    def winforms_Resize(self, sender, event):
+        self.resize_content()
+
     def winforms_FormClosing(self, sender, event):
         # If the app is exiting, or a manual close has been requested, don't get
         # confirmation; just close.