diff --git a/novaclient/__init__.py b/novaclient/__init__.py
index 8b6111de1..304660c93 100644
--- a/novaclient/__init__.py
+++ b/novaclient/__init__.py
@@ -25,4 +25,4 @@ API_MIN_VERSION = api_versions.APIVersion("2.1")
 # when client supported the max version, and bumped sequentially, otherwise
 # the client may break due to server side new version may include some
 # backward incompatible change.
-API_MAX_VERSION = api_versions.APIVersion("2.72")
+API_MAX_VERSION = api_versions.APIVersion("2.73")
diff --git a/novaclient/tests/unit/fixture_data/servers.py b/novaclient/tests/unit/fixture_data/servers.py
index 6df4129bd..d3354469a 100644
--- a/novaclient/tests/unit/fixture_data/servers.py
+++ b/novaclient/tests/unit/fixture_data/servers.py
@@ -454,6 +454,8 @@ class V1(Base):
             pass
         elif action == 'migrate':
             return None
+        elif action == 'lock':
+            return None
         elif action == 'rebuild':
             body = body[action]
             adminPass = body.get('adminPass', 'randompassword')
diff --git a/novaclient/tests/unit/v2/fakes.py b/novaclient/tests/unit/v2/fakes.py
index a32e22582..29ec88877 100644
--- a/novaclient/tests/unit/v2/fakes.py
+++ b/novaclient/tests/unit/v2/fakes.py
@@ -774,7 +774,7 @@ class FakeSessionClient(base_client.SessionClient):
 
     none_actions = ['revertResize', 'os-stop', 'os-start',
                     'forceDelete', 'restore', 'pause', 'unpause', 'unlock',
-                    'unrescue', 'resume', 'suspend', 'lock', 'shelve',
+                    'unrescue', 'resume', 'suspend', 'shelve',
                     'shelveOffload', 'unshelve', 'resetNetwork']
     type_actions = ['os-getVNCConsole', 'os-getSPICEConsole',
                     'os-getRDPConsole']
@@ -836,6 +836,22 @@ class FakeSessionClient(base_client.SessionClient):
                     # host can be optional
                     expected.add('host')
                 assert set(body[action].keys()) == expected
+        elif action == 'lock':
+            if self.api_version < api_versions.APIVersion("2.73"):
+                assert body[action] is None
+            else:
+                # In 2.73 and above, we allow body to be one of these:
+                # a) {'lock': None}
+                # b) {'lock': {}}
+                # c) {'lock': {locked_reason': 'blah'}}
+                if body[action] is not None:
+                    expected = set()
+                    if 'locked_reason' in body[action].keys():
+                        # reason can be optional
+                        expected.add('locked_reason')
+                    assert set(body[action].keys()) == expected
+                else:
+                    assert body[action] is None
         elif action == 'rebuild':
             body = body[action]
             adminPass = body.get('adminPass', 'randompassword')
diff --git a/novaclient/tests/unit/v2/test_servers.py b/novaclient/tests/unit/v2/test_servers.py
index 529fd389d..43dbf2c28 100644
--- a/novaclient/tests/unit/v2/test_servers.py
+++ b/novaclient/tests/unit/v2/test_servers.py
@@ -1703,3 +1703,26 @@ class ServersV268Test(ServersV267Test):
         ex = self.assertRaises(TypeError, self.cs.servers.live_migrate,
                                host='hostname', force=True)
         self.assertIn('force', six.text_type(ex))
+
+
+class ServersV273Test(ServersV268Test):
+
+    api_version = "2.73"
+
+    def test_lock_server(self):
+        s = self.cs.servers.get(1234)
+        ret = s.lock()
+        self.assert_request_id(ret, fakes.FAKE_REQUEST_ID_LIST)
+        self.assert_called('POST', '/servers/1234/action',
+                           {'lock': None})
+        ret = s.lock(reason='zombie-apocalypse')
+        self.assert_request_id(ret, fakes.FAKE_REQUEST_ID_LIST)
+        self.assert_called('POST', '/servers/1234/action',
+                           {'lock': {'locked_reason': 'zombie-apocalypse'}})
+
+    def test_lock_server_pre_273_fails_with_reason(self):
+        self.cs.api_version = api_versions.APIVersion('2.72')
+        s = self.cs.servers.get(1234)
+        e = self.assertRaises(TypeError,
+                              s.lock, reason='blah')
+        self.assertIn("unexpected keyword argument 'reason'", six.text_type(e))
diff --git a/novaclient/tests/unit/v2/test_shell.py b/novaclient/tests/unit/v2/test_shell.py
index 447a7229f..4f2ee2582 100644
--- a/novaclient/tests/unit/v2/test_shell.py
+++ b/novaclient/tests/unit/v2/test_shell.py
@@ -2092,6 +2092,24 @@ class ShellTest(utils.TestCase):
         self.run_command('lock sample-server')
         self.assert_called('POST', '/servers/1234/action', {'lock': None})
 
+    def test_lock_pre_v273(self):
+        exp = self.assertRaises(SystemExit,
+                                self.run_command,
+                                'lock sample-server --reason zombies',
+                                api_version='2.72')
+        self.assertIn('2', six.text_type(exp))
+
+    def test_lock_v273(self):
+        self.run_command('lock sample-server',
+                         api_version='2.73')
+        self.assert_called('POST', '/servers/1234/action',
+                           {'lock': None})
+
+        self.run_command('lock sample-server --reason zombies',
+                         api_version='2.73')
+        self.assert_called('POST', '/servers/1234/action',
+                           {'lock': {'locked_reason': 'zombies'}})
+
     def test_unlock(self):
         self.run_command('unlock sample-server')
         self.assert_called('POST', '/servers/1234/action', {'unlock': None})
@@ -4280,6 +4298,22 @@ class ShellTest(utils.TestCase):
         self.assert_called('GET', '/servers/9015', pos=2)
         self.assert_called('GET', '/v2/images/%s' % FAKE_UUID_2, pos=3)
 
+    def test_list_pre_v273(self):
+        exp = self.assertRaises(SystemExit,
+                                self.run_command,
+                                'list --locked t',
+                                api_version='2.72')
+        self.assertEqual(2, exp.code)
+
+    def test_list_v273(self):
+        self.run_command('list --locked t', api_version='2.73')
+        self.assert_called('GET', '/servers/detail?locked=t')
+
+    def test_list_v273_with_sort_key_dir(self):
+        self.run_command('list --sort locked:asc', api_version='2.73')
+        self.assert_called(
+            'GET', '/servers/detail?sort_dir=asc&sort_key=locked')
+
 
 class PollForStatusTestCase(utils.TestCase):
     @mock.patch("novaclient.v2.shell.time")
diff --git a/novaclient/v2/servers.py b/novaclient/v2/servers.py
index a37c1b387..afbd5536c 100644
--- a/novaclient/v2/servers.py
+++ b/novaclient/v2/servers.py
@@ -214,6 +214,7 @@ class Server(base.Resource):
         """
         return self.manager.unpause(self)
 
+    @api_versions.wraps("2.0", "2.72")
     def lock(self):
         """
         Lock -- Lock the instance from certain operations.
@@ -222,6 +223,16 @@ class Server(base.Resource):
         """
         return self.manager.lock(self)
 
+    @api_versions.wraps("2.73")
+    def lock(self, reason=None):
+        """
+        Lock -- Lock the instance from certain operations.
+
+        :param reason: (Optional) The lock reason.
+        :returns: An instance of novaclient.base.TupleWithMeta
+        """
+        return self.manager.lock(self, reason=reason)
+
     def unlock(self):
         """
         Unlock -- Remove instance lock.
@@ -1097,6 +1108,7 @@ class ServerManager(base.BootingManagerWithFind):
         """
         return self._action('unpause', server, None)
 
+    @api_versions.wraps("2.0", "2.72")
     def lock(self, server):
         """
         Lock the server.
@@ -1106,6 +1118,22 @@ class ServerManager(base.BootingManagerWithFind):
         """
         return self._action('lock', server, None)
 
+    @api_versions.wraps("2.73")
+    def lock(self, server, reason=None):
+        """
+        Lock the server.
+
+        :param server: The :class:`Server` (or its ID) to lock
+        :param reason: (Optional) The lock reason.
+        :returns: An instance of novaclient.base.TupleWithMeta
+        """
+        info = None
+
+        if reason:
+            info = {'locked_reason': reason}
+
+        return self._action('lock', server, info)
+
     def unlock(self, server):
         """
         Unlock the server.
diff --git a/novaclient/v2/shell.py b/novaclient/v2/shell.py
index f7d59dfaa..4e8a730d3 100644
--- a/novaclient/v2/shell.py
+++ b/novaclient/v2/shell.py
@@ -1563,6 +1563,13 @@ def _print_flavor(flavor):
            "case is 'NOT(t1 OR t2)'. Tags must be separated by commas: "
            "--not-tags-any <tag1,tag2>"),
     start_version="2.26")
+@utils.arg(
+    '--locked',
+    dest='locked',
+    metavar='<locked>',
+    default=None,
+    help=_('Display servers based on their locked value'),
+    start_version="2.73")
 def do_list(cs, args):
     """List servers."""
     imageid = None
@@ -1639,6 +1646,11 @@ def do_list(cs, args):
             raise exceptions.CommandError(_('Invalid changes-before value: %s')
                                           % search_opts['changes-before'])
 
+    # In microversion 2.73 we added ``locked`` option in server details.
+    have_added_locked = cs.api_version >= api_versions.APIVersion('2.73')
+    if have_added_locked and args.locked:
+        search_opts['locked'] = args.locked
+
     servers = cs.servers.list(detailed=detailed,
                               search_opts=search_opts,
                               sort_keys=sort_keys,
@@ -2155,12 +2167,23 @@ def do_start(cs, args):
         _("Unable to start the specified server(s)."))
 
 
+# From microversion 2.73, we can specify a reason for locking the server.
 @utils.arg('server', metavar='<server>', help=_('Name or ID of server.'))
+@utils.arg(
+    '--reason',
+    metavar='<reason>',
+    help=_('Reason for locking the server.'),
+    start_version='2.73')
 def do_lock(cs, args):
     """Lock a server. A normal (non-admin) user will not be able to execute
     actions on a locked server.
     """
-    _find_server(cs, args.server).lock()
+    update_kwargs = {}
+    if 'reason' in args and args.reason is not None:
+        update_kwargs['reason'] = args.reason
+
+    server = _find_server(cs, args.server)
+    server.lock(**update_kwargs)
 
 
 @utils.arg('server', metavar='<server>', help=_('Name or ID of server.'))
diff --git a/releasenotes/notes/bp-add-locked-reason-3f136db97b820c73.yaml b/releasenotes/notes/bp-add-locked-reason-3f136db97b820c73.yaml
new file mode 100644
index 000000000..60e19bfcf
--- /dev/null
+++ b/releasenotes/notes/bp-add-locked-reason-3f136db97b820c73.yaml
@@ -0,0 +1,6 @@
+---
+features:
+  - Added a ``--reason`` option to ``nova lock`` command that enables users
+    to specify a reason when locking a server and a ``locked``
+    filtering/sorting option to ``nova list`` command which enables users to
+    filter/sort servers based on their ``locked`` value in microversion 2.73.