diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -445,6 +445,66 @@ class ThreadTests(BaseTestCase):
         self.assertEqual(out, b'')
         self.assertEqual(err, b'')
 
+    def test_main_thread(self):
+        main = threading.main_thread()
+        self.assertEqual(main.name, 'MainThread')
+        self.assertEqual(main.ident, threading.current_thread().ident)
+        self.assertEqual(main.ident, threading.get_ident())
+
+        def f():
+            self.assertNotEqual(threading.main_thread().ident,
+                                threading.current_thread().ident)
+        th = threading.Thread(target=f)
+        th.start()
+        th.join()
+
+    @unittest.skipUnless(hasattr(os, 'fork'), "test needs os.fork()")
+    @unittest.skipUnless(hasattr(os, 'waitpid'), "test needs os.waitpid()")
+    def test_main_thread_after_fork(self):
+        code = """if 1:
+            import os, threading
+
+            pid = os.fork()
+            if pid == 0:
+                main = threading.main_thread()
+                print(main.name)
+                print(main.ident == threading.current_thread().ident)
+                print(main.ident == threading.get_ident())
+            else:
+                os.waitpid(pid, 0)
+        """
+        rc, out, err = assert_python_ok("-c", code)
+        self.assertEqual(rc, 0)
+        data = out.decode().replace('\r', '')
+        self.assertEqual(err, b"")
+        self.assertEqual(data, "MainThread\nTrue\nTrue\n")
+
+    @unittest.skipUnless(hasattr(os, 'fork'), "test needs os.fork()")
+    @unittest.skipUnless(hasattr(os, 'waitpid'), "test needs os.waitpid()")
+    def test_main_thread_after_fork_from_nonmain_thread(self):
+        code = """if 1:
+            import os, threading
+
+            def f():
+                pid = os.fork()
+                if pid == 0:
+                    main = threading.main_thread()
+                    print(main.name)
+                    print(main.ident == threading.current_thread().ident)
+                    print(main.ident == threading.get_ident())
+                else:
+                    os.waitpid(pid, 0)
+
+            th = threading.Thread(target=f)
+            th.start()
+            th.join()
+        """
+        rc, out, err = assert_python_ok("-c", code)
+        self.assertEqual(rc, 0)
+        data = out.decode().replace('\r', '')
+        self.assertEqual(err, b"")
+        self.assertEqual(data, "MainThread\nTrue\nTrue\n")
+
 
 class ThreadJoinOnShutdown(BaseTestCase):
 
diff --git a/Lib/threading.py b/Lib/threading.py
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -915,7 +915,12 @@ from _thread import stack_size
 # and make it available for the interpreter
 # (Py_Main) as threading._shutdown.
 
-_shutdown = _MainThread()._exitfunc
+_main_thread = _MainThread()
+
+def main_thread():
+    return _main_thread
+
+_shutdown = _main_thread._exitfunc
 
 # get thread-local implementation, either from the thread
 # module, or from the python fallback