diff --git a/patrole_tempest_plugin/config.py b/patrole_tempest_plugin/config.py
index 47b76d4..5818843 100644
--- a/patrole_tempest_plugin/config.py
+++ b/patrole_tempest_plugin/config.py
@@ -39,8 +39,9 @@
                 help="""List of the paths to search for policy files. Each
 policy path assumes that the service name is included in the path once. Also
 assumes Patrole is on the same host as the policy files. The paths should be
-ordered by precedence, with high-priority paths before low-priority paths. The
-first path that is found to contain the service's policy file will be used.
+ordered by precedence, with high-priority paths before low-priority paths. All
+the paths that are found to contain the service's policy file will be used and
+all policy files will be merged.
 """),
     cfg.BoolOpt('test_custom_requirements',
                 default=False,
diff --git a/patrole_tempest_plugin/policy_authority.py b/patrole_tempest_plugin/policy_authority.py
index 3339a5d..27786ae 100644
--- a/patrole_tempest_plugin/policy_authority.py
+++ b/patrole_tempest_plugin/policy_authority.py
@@ -13,7 +13,9 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import collections
 import copy
+import glob
 import json
 import os
 
@@ -103,17 +105,14 @@
         if extra_target_data is None:
             extra_target_data = {}
 
-        self.validate_service(service)
+        self.service = self.validate_service(service)
 
         # Prioritize dynamically searching for policy files over relying on
         # deprecated service-specific policy file locations.
-        self.path = None
         if CONF.patrole.custom_policy_files:
             self.discover_policy_files()
-            self.path = self.policy_files.get(service)
 
-        self.rules = policy.Rules.load(self._get_policy_data(service),
-                                       'default')
+        self.rules = policy.Rules.load(self._get_policy_data(), 'default')
         self.project_id = project_id
         self.user_id = user_id
         self.extra_target_data = extra_target_data
@@ -139,19 +138,22 @@
             raise rbac_exceptions.RbacInvalidServiceException(
                 "%s is NOT a valid service." % service)
 
+        return service
+
     @classmethod
     def discover_policy_files(cls):
         """Dynamically discover the policy file for each service in
-        ``cls.available_services``. Pick the first candidate path found
+        ``cls.available_services``. Pick all candidate paths found
         out of the potential paths in ``[patrole] custom_policy_files``.
         """
         if not hasattr(cls, 'policy_files'):
-            cls.policy_files = {}
+            cls.policy_files = collections.defaultdict(list)
             for service in cls.available_services:
                 for candidate_path in CONF.patrole.custom_policy_files:
-                    if os.path.isfile(candidate_path % service):
-                        cls.policy_files.setdefault(service,
-                                                    candidate_path % service)
+                    path = candidate_path % service
+                    for filename in glob.iglob(path):
+                        if os.path.isfile(filename):
+                            cls.policy_files[service].append(filename)
 
     def allowed(self, rule_name, role):
         """Checks if a given rule in a policy is allowed with given role.
@@ -168,17 +170,28 @@
             is_admin=is_admin_context)
         return is_allowed
 
-    def _get_policy_data(self, service):
+    def _get_policy_data(self):
         file_policy_data = {}
         mgr_policy_data = {}
         policy_data = {}
 
         # Check whether policy file exists and attempt to read it.
-        if self.path and os.path.isfile(self.path):
+        for path in self.policy_files[self.service]:
             try:
-                with open(self.path, 'r') as policy_file:
-                    file_policy_data = policy_file.read()
-                file_policy_data = json.loads(file_policy_data)
+                with open(path, 'r') as fp:
+                    for k, v in json.load(fp).items():
+                        if k not in file_policy_data:
+                            file_policy_data[k] = v
+                        else:
+                            # If the policy name and rule are the same, no
+                            # ambiguity, so no reason to warn.
+                            if v != file_policy_data[k]:
+                                LOG.warning(
+                                    "The same policy name: %s was found in "
+                                    "multiple policies files for service %s. "
+                                    "This can lead to policy rule ambiguity. "
+                                    "Using rule: %s", k, self.service,
+                                    file_policy_data[k])
             except (IOError, ValueError) as e:
                 msg = "Failed to read policy file for service. "
                 if isinstance(e, IOError):
@@ -186,21 +199,20 @@
                 else:
                     msg += "JSON may be improperly formatted."
                 LOG.debug(msg)
-                file_policy_data = {}
 
         # Check whether policy actions are defined in code. Nova and Keystone,
         # for example, define their default policy actions in code.
         mgr = stevedore.named.NamedExtensionManager(
             'oslo.policy.policies',
-            names=[service],
+            names=[self.service],
             on_load_failure_callback=None,
             invoke_on_load=True,
             warn_on_missing_entrypoint=False)
 
         if mgr:
-            policy_generator = {policy.name: policy.obj for policy in mgr}
-            if policy_generator and service in policy_generator:
-                for rule in policy_generator[service]:
+            policy_generator = {plc.name: plc.obj for plc in mgr}
+            if policy_generator and self.service in policy_generator:
+                for rule in policy_generator[self.service]:
                     mgr_policy_data[rule.name] = str(rule.check)
 
         # If data from both file and code exist, combine both together.
@@ -217,10 +229,10 @@
             policy_data = mgr_policy_data
         else:
             error_message = (
-                'Policy file for {0} service was not found among the '
+                'Policy files for {0} service were not found among the '
                 'registered in-code policies or in any of the possible policy '
-                'files: {1}.'.format(service,
-                                     [loc % service for loc in
+                'files: {1}.'.format(self.service,
+                                     [loc % self.service for loc in
                                       CONF.patrole.custom_policy_files])
             )
             raise rbac_exceptions.RbacParsingException(error_message)
@@ -228,8 +240,8 @@
         try:
             policy_data = json.dumps(policy_data)
         except (TypeError, ValueError):
-            error_message = 'Policy file for {0} service is invalid.'.format(
-                service)
+            error_message = 'Policy files for {0} service are invalid.'.format(
+                self.service)
             raise rbac_exceptions.RbacParsingException(error_message)
 
         return policy_data
@@ -296,9 +308,11 @@
 
     def _try_rule(self, apply_rule, target, access_data, o):
         if apply_rule not in self.rules:
-            message = ("Policy action \"{0}\" not found in policy file: {1} or"
-                       " among registered policy in code defaults for service."
-                       ).format(apply_rule, self.path)
+            message = ('Policy action "{0}" not found in policy files: '
+                       '{1} or among registered policy in code defaults for '
+                       '{2} service.').format(apply_rule,
+                                              self.policy_files[self.service],
+                                              self.service)
             LOG.debug(message)
             raise rbac_exceptions.RbacParsingException(message)
         else:
diff --git a/patrole_tempest_plugin/tests/unit/test_policy_authority.py b/patrole_tempest_plugin/tests/unit/test_policy_authority.py
index d396a29..b2af1c6 100644
--- a/patrole_tempest_plugin/tests/unit/test_policy_authority.py
+++ b/patrole_tempest_plugin/tests/unit/test_policy_authority.py
@@ -270,9 +270,9 @@
 
         fake_rule = 'fake_rule'
         expected_message = (
-            "Policy action \"{0}\" not found in policy file: {1} or among "
-            "registered policy in code defaults for service.").format(
-            fake_rule, self.custom_policy_file)
+            'Policy action "{0}" not found in policy files: {1} or among '
+            'registered policy in code defaults for {2} service.').format(
+            fake_rule, [self.custom_policy_file], "custom_rbac_policy")
 
         e = self.assertRaises(rbac_exceptions.RbacParsingException,
                               authority.allowed, fake_rule, None)
@@ -292,9 +292,10 @@
                mock.sentinel.error)})
 
         expected_message = (
-            "Policy action \"{0}\" not found in policy file: {1} or among "
-            "registered policy in code defaults for service.").format(
-            mock.sentinel.rule, self.custom_policy_file)
+            'Policy action "{0}" not found in policy files: {1} or among '
+            'registered policy in code defaults for {2} service.').format(
+            mock.sentinel.rule, [self.custom_policy_file],
+            "custom_rbac_policy")
 
         e = self.assertRaises(rbac_exceptions.RbacParsingException,
                               authority.allowed, mock.sentinel.rule, None)
@@ -313,7 +314,7 @@
         ]
 
         mock_manager = mock.Mock(obj=fake_policy_rules, __name__='foo')
-        mock_manager.configure_mock(name='fake_service')
+        mock_manager.configure_mock(name='tenant_rbac_policy')
         mock_stevedore.named.NamedExtensionManager.return_value = [
             mock_manager
         ]
@@ -323,7 +324,7 @@
         authority = policy_authority.PolicyAuthority(
             test_tenant_id, test_user_id, "tenant_rbac_policy")
 
-        policy_data = authority._get_policy_data('fake_service')
+        policy_data = authority._get_policy_data()
         self.assertIsInstance(policy_data, str)
 
         actual_policy_data = json.loads(policy_data)
@@ -354,7 +355,7 @@
         ]
 
         mock_manager = mock.Mock(obj=fake_policy_rules, __name__='foo')
-        mock_manager.configure_mock(name='fake_service')
+        mock_manager.configure_mock(name='tenant_rbac_policy')
         mock_stevedore.named.NamedExtensionManager.return_value = [
             mock_manager
         ]
@@ -364,7 +365,7 @@
 
         authority = policy_authority.PolicyAuthority(
             test_tenant_id, test_user_id, 'tenant_rbac_policy')
-        policy_data = authority._get_policy_data('fake_service')
+        policy_data = authority._get_policy_data()
         self.assertIsInstance(policy_data, str)
 
         actual_policy_data = json.loads(policy_data)
@@ -388,7 +389,7 @@
                               None, None, 'test_service')
 
         expected_error = (
-            'Policy file for {0} service was not found among the registered '
+            'Policy files for {0} service were not found among the registered '
             'in-code policies or in any of the possible policy files: {1}.'
             .format('test_service',
                     [CONF.patrole.custom_policy_files[0] % 'test_service']))
@@ -413,7 +414,7 @@
                               policy_authority.PolicyAuthority,
                               None, None, 'test_service')
 
-        expected_error = "Policy file for {0} service is invalid."\
+        expected_error = "Policy files for {0} service are invalid."\
                          .format("test_service")
         self.assertIn(expected_error, str(e))
 
@@ -435,7 +436,7 @@
                               None, None, 'tenant_rbac_policy')
 
         expected_error = (
-            'Policy file for {0} service was not found among the registered '
+            'Policy files for {0} service were not found among the registered '
             'in-code policies or in any of the possible policy files: {1}.'
             .format('tenant_rbac_policy', [CONF.patrole.custom_policy_files[0]
                                            % 'tenant_rbac_policy']))
@@ -450,7 +451,7 @@
                       dir(policy_authority.PolicyAuthority))
         self.assertIn('policy_files', dir(policy_parser))
         self.assertIn('tenant_rbac_policy', policy_parser.policy_files)
-        self.assertEqual(self.conf_policy_path % 'tenant_rbac_policy',
+        self.assertEqual([self.conf_policy_path % 'tenant_rbac_policy'],
                          policy_parser.policy_files['tenant_rbac_policy'])
 
     @mock.patch.object(policy_authority, 'policy', autospec=True)
@@ -458,35 +459,40 @@
                        autospec=True)
     @mock.patch.object(policy_authority, 'clients', autospec=True)
     @mock.patch.object(policy_authority, 'os', autospec=True)
-    def test_discover_policy_files_with_many_invalid_one_valid(self, m_os,
-                                                               m_creds, *args):
+    @mock.patch.object(policy_authority, 'glob', autospec=True)
+    def test_discover_policy_files_with_many_invalid_one_valid(self, m_glob,
+                                                               m_os, m_creds,
+                                                               *args):
+        service = 'test_service'
+        custom_policy_files = ['foo/%s', 'bar/%s', 'baz/%s']
+        m_glob.iglob.side_effect = [iter([path % service])
+                                    for path in custom_policy_files]
         # Only the 3rd path is valid.
-        m_os.path.isfile.side_effect = [False, False, True, False]
+        m_os.path.isfile.side_effect = [False, False, True]
 
         # Ensure the outer for loop runs only once in `discover_policy_files`.
         m_creds.Manager().identity_services_v3_client.\
             list_services.return_value = {
-                'services': [{'name': 'test_service'}]}
+                'services': [{'name': service}]}
 
         # The expected policy will be 'baz/test_service'.
         self.useFixture(fixtures.ConfPatcher(
-            custom_policy_files=['foo/%s', 'bar/%s', 'baz/%s'],
+            custom_policy_files=custom_policy_files,
             group='patrole'))
 
         policy_parser = policy_authority.PolicyAuthority(
-            None, None, 'test_service')
+            None, None, service)
 
         # Ensure that "policy_files" is set at class and instance levels.
-        self.assertIn('policy_files',
-                      dir(policy_authority.PolicyAuthority))
-        self.assertIn('policy_files', dir(policy_parser))
-        self.assertIn('test_service', policy_parser.policy_files)
-        self.assertEqual('baz/test_service',
-                         policy_parser.policy_files['test_service'])
+        self.assertTrue(hasattr(policy_authority.PolicyAuthority,
+                                'policy_files'))
+        self.assertTrue(hasattr(policy_parser, 'policy_files'))
+        self.assertEqual(['baz/%s' % service],
+                         policy_parser.policy_files[service])
 
     def test_discover_policy_files_with_no_valid_files(self):
         expected_error = (
-            'Policy file for {0} service was not found among the registered '
+            'Policy files for {0} service were not found among the registered '
             'in-code policies or in any of the possible policy files: {1}.'
             .format('test_service', [self.conf_policy_path % 'test_service']))
 
@@ -495,11 +501,11 @@
                               None, None, 'test_service')
         self.assertIn(expected_error, str(e))
 
-        self.assertIn('policy_files',
-                      dir(policy_authority.PolicyAuthority))
-        self.assertNotIn(
-            'test_service',
-            policy_authority.PolicyAuthority.policy_files.keys())
+        self.assertTrue(hasattr(policy_authority.PolicyAuthority,
+                                'policy_files'))
+        self.assertEqual(
+            [],
+            policy_authority.PolicyAuthority.policy_files['test_service'])
 
     def _test_validate_service(self, v2_services, v3_services,
                                expected_failure=False, expected_services=None):
diff --git a/releasenotes/notes/multiple-policy-files-9aa7f7583283739e.yaml b/releasenotes/notes/multiple-policy-files-9aa7f7583283739e.yaml
new file mode 100644
index 0000000..a3555e6
--- /dev/null
+++ b/releasenotes/notes/multiple-policy-files-9aa7f7583283739e.yaml
@@ -0,0 +1,17 @@
+---
+features:
+  - |
+    In order to implement the tests for plugins which do not maintain the
+    ``policy.json`` with full list of the policy rules and provide policy file
+    with only their own policy rules, the Patrole should be able to load and
+    merge multiple policy files for any of the services.
+
+    - Discovery all policy files for each of the services.
+      The updated ``discover_policy_files`` function picks all candidate paths
+      found out of the potential paths in the ``[patrole].custom_policy_files``
+      config option. Using ``glob.glob()`` function makes it possible to use
+      the patterns like '\*.json' to discover the policy files.
+
+    - Loading and merging a data from multiple policy files.
+      Patrole loads a data from each of the discovered policy files for a
+      service and merge the data from all files.