diff --git a/pyproject.toml b/pyproject.toml
index cb27f399..18bf0526 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -23,3 +23,9 @@ build-backend = "setuptools.build_meta"
 
 [tool.setuptools_scm]
 write_to = "src/pgzero/_version.py"
+
+[tool.ruff]
+builtins = [
+    "Actor", "Rect", "ZRect", "animate", "clock", "exit", "images", "keyboard", "keymods",
+    "keys", "mouse", "music", "screen", "sounds", "storage", "tone"
+]
diff --git a/src/pgzero/runner.py b/src/pgzero/runner.py
index b4166f76..adeaf64e 100644
--- a/src/pgzero/runner.py
+++ b/src/pgzero/runner.py
@@ -69,30 +69,75 @@ def main():
         help="Print periodic FPS measurements on the terminal."
     )
     parser.add_argument(
-        'program',
-        help="The Pygame Zero program to run."
+        'game',
+        help="The Pygame Zero game to run (a Python file or directory)."
     )
     args = parser.parse_args()
 
     if __debug__:
         warnings.simplefilter('default', DeprecationWarning)
 
-    load_and_run(args.program, fps=args.fps)
+    try:
+        load_and_run(args.game, fps=args.fps)
+    except NoMainModule as e:
+        sys.exit(e)
+
+
+class NoMainModule(Exception):
+    """Indicate that we couldn't find a main module to run."""
 
 
 def load_and_run(path, *, fps: bool = False):
-    """Load and run the given Python file as the main PGZero game module.
+    """Load and run the given Python file or directory.
+
+    If a file, run this as the main PGZero game module.
+
+    If a directory, run the first file inside the directory containing:
+
+    * `__main__.py`
+    * `main.py`
+    * `run_game.py`
+    * `<name>.py` where `<name>` is the basename of the directory
 
     Note that the 'import pgzrun' IDE mode doesn't pass through this entry
     point, as the module is already loaded.
 
     """
-    with open(path, 'rb') as f:
-        src = f.read()
+    path = path.rstrip(os.sep)
+    try:
+        with open(path, 'rb') as f:
+            src = f.read()
+    except FileNotFoundError:
+        raise NoMainModule(f"Error: {path} does not exist.")
+    except IsADirectoryError:
+        name = os.path.basename(path)
+        for candidate in (
+            '__main__.py',
+            'main.py',
+            'run_game.py',
+            f'{name}.py'
+        ):
+            try:
+                with open(os.path.join(path, candidate), 'rb') as f:
+                    src = f.read()
+                    break
+            except FileNotFoundError:
+                pass
+        else:
+            raise NoMainModule(f"""\
+Error: {path} is a directory.
+
+To run a directory with pgzrun, it must contain a file named __main__.py,
+main.py, run_game.py, or a .py file with the same name as the directory.
+
+You can also run a specific file with:
+
+    pgzrun path/to/your/file.py
+""")
+    else:
+        name, _ = os.path.splitext(os.path.basename(path))
 
     code = compile(src, os.path.basename(path), 'exec', dont_inherit=True)
-
-    name, _ = os.path.splitext(os.path.basename(path))
     mod = ModuleType(name)
     mod.__file__ = path
     mod.__name__ = name
diff --git a/test/game_tests/blue/run_game.py b/test/game_tests/blue/run_game.py
new file mode 100644
index 00000000..dd552e3a
--- /dev/null
+++ b/test/game_tests/blue/run_game.py
@@ -0,0 +1,2 @@
+def draw():
+    screen.fill('blue')
diff --git a/test/game_tests/green/green.py b/test/game_tests/green/green.py
new file mode 100644
index 00000000..3f99ef4b
--- /dev/null
+++ b/test/game_tests/green/green.py
@@ -0,0 +1,2 @@
+def draw():
+    screen.fill('green')
diff --git a/test/game_tests/pink/main.py b/test/game_tests/pink/main.py
new file mode 100644
index 00000000..20c326e1
--- /dev/null
+++ b/test/game_tests/pink/main.py
@@ -0,0 +1,2 @@
+def draw():
+    screen.fill('pink')
diff --git a/test/game_tests/red/__main__.py b/test/game_tests/red/__main__.py
new file mode 100644
index 00000000..6b1ccf61
--- /dev/null
+++ b/test/game_tests/red/__main__.py
@@ -0,0 +1,2 @@
+def draw():
+    screen.fill('red')
diff --git a/test/test_runner.py b/test/test_runner.py
index 4f1b33c7..2976046e 100644
--- a/test/test_runner.py
+++ b/test/test_runner.py
@@ -16,14 +16,32 @@
 class RunnerTest(unittest.TestCase):
     """Test that we can load and run the current file."""
 
-    def test_run(self):
-        """We can load and run a game saved as UTF-8."""
+    def assert_runnable(self, path: Path):
+        """Check that we can run the given file."""
         clock.schedule_unique(sys.exit, 0.05)
         with self.assertRaises(SystemExit):
-            load_and_run(str(game_tests / 'utf8.py'))
+            load_and_run(str(path))
+
+    def test_run_utf8(self):
+        """We can load and run a game saved as UTF-8."""
+        self.assert_runnable(game_tests / 'utf8.py')
 
     def test_import(self):
         """Games can import other modules, which can acccess the builtins."""
-        clock.schedule_unique(sys.exit, 0.05)
-        with self.assertRaises(SystemExit):
-            load_and_run(str(game_tests / 'importing.py'))
+        self.assert_runnable(game_tests / 'importing.py')
+
+    def test_run_directory_dunder_main(self):
+        """We can run a directory containing __main__.py"""
+        self.assert_runnable(game_tests / 'red')
+
+    def test_run_directory_main(self):
+        """We can run a directory containing main.py"""
+        self.assert_runnable(game_tests / 'pink')
+
+    def test_run_directory_ane_name(self):
+        """We can run a directory containing <basename>.py"""
+        self.assert_runnable(game_tests / 'green')
+
+    def test_run_directory_run_game(self):
+        """We can run a directory containing run_game.py"""
+        self.assert_runnable(game_tests / 'blue')