diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index f466614061..7a5551f650 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -594,6 +594,12 @@ class ModelAdmin(BaseModelAdmin):
     def __str__(self):
         return "%s.%s" % (self.model._meta.app_label, self.__class__.__name__)
 
+    def __repr__(self):
+        return (
+            f'<{self.__class__.__qualname__}: model={self.model.__qualname__} '
+            f'site={self.admin_site!r}>'
+        )
+
     def get_inline_instances(self, request, obj=None):
         inline_instances = []
         for inline_class in self.get_inlines(request, obj):
diff --git a/django/contrib/admin/sites.py b/django/contrib/admin/sites.py
index 62c5c8a782..a87bac02bd 100644
--- a/django/contrib/admin/sites.py
+++ b/django/contrib/admin/sites.py
@@ -77,6 +77,9 @@ class AdminSite:
         self._global_actions = self._actions.copy()
         all_sites.add(self)
 
+    def __repr__(self):
+        return f'{self.__class__.__name__}(name={self.name!r})'
+
     def check(self, app_configs):
         """
         Run the system checks on all ModelAdmins, except if they aren't
@@ -561,6 +564,9 @@ class DefaultAdminSite(LazyObject):
         AdminSiteClass = import_string(apps.get_app_config('admin').default_site)
         self._wrapped = AdminSiteClass()
 
+    def __repr__(self):
+        return repr(self._wrapped)
+
 
 # This global object represents the default admin site, for the common case.
 # You can provide your own AdminSite using the (Simple)AdminConfig.default_site
diff --git a/tests/admin_default_site/tests.py b/tests/admin_default_site/tests.py
index 5d05ec9c45..9ce087549f 100644
--- a/tests/admin_default_site/tests.py
+++ b/tests/admin_default_site/tests.py
@@ -2,6 +2,8 @@ from django.contrib import admin
 from django.contrib.admin import sites
 from django.test import SimpleTestCase, override_settings
 
+from .sites import CustomAdminSite
+
 
 @override_settings(INSTALLED_APPS=[
     'admin_default_site.apps.MyCustomAdminConfig',
@@ -29,3 +31,13 @@ class CustomAdminSiteTests(SimpleTestCase):
 class DefaultAdminSiteTests(SimpleTestCase):
     def test_use_default_admin_site(self):
         self.assertEqual(admin.site.__class__.__name__, 'AdminSite')
+
+    def test_repr(self):
+        self.assertEqual(str(admin.site), "AdminSite(name='admin')")
+        self.assertEqual(repr(admin.site), "AdminSite(name='admin')")
+
+
+class AdminSiteTests(SimpleTestCase):
+    def test_repr(self):
+        admin_site = CustomAdminSite(name='other')
+        self.assertEqual(repr(admin_site), "CustomAdminSite(name='other')")
diff --git a/tests/modeladmin/tests.py b/tests/modeladmin/tests.py
index 00de9f7523..42cc369a9e 100644
--- a/tests/modeladmin/tests.py
+++ b/tests/modeladmin/tests.py
@@ -722,6 +722,13 @@ class ModelAdminTests(TestCase):
         self.assertEqual(perms_needed, {'band'})
         self.assertEqual(protected, [])
 
+    def test_modeladmin_repr(self):
+        ma = ModelAdmin(Band, self.site)
+        self.assertEqual(
+            repr(ma),
+            "<ModelAdmin: model=Band site=AdminSite(name='admin')>",
+        )
+
 
 class ModelAdminPermissionTests(SimpleTestCase):