diff --git a/common/lib/xmodule/xmodule/course_module.py b/common/lib/xmodule/xmodule/course_module.py
index 73bc5e656a..bf23e31bab 100644
--- a/common/lib/xmodule/xmodule/course_module.py
+++ b/common/lib/xmodule/xmodule/course_module.py
@@ -271,6 +271,33 @@ def get_available_providers():
     return available_providers
 
 
+class TeamsConfigField(Dict):
+    """
+    XBlock field for teams configuration, including definitions for teamsets.
+
+    Serializes to JSON dictionary.
+    """
+    _default = TeamsConfig({})
+
+    def from_json(self, value):
+        """
+        Return a TeamsConfig instance from a dict.
+        """
+        return TeamsConfig(value)
+
+    def to_json(self, value):
+        """
+        Convert a TeamsConfig instance back to a dict.
+
+        If we have the data that was used to build the TeamsConfig instance,
+        return that instead of `value.cleaned_data`, thus preserving the
+        data in the form that the user entered it.
+        """
+        if value.source_data is not None:
+            return value.source_data
+        return value.cleaned_data
+
+
 class CourseFields(object):
     lti_passports = List(
         display_name=_("LTI Passports"),
@@ -797,7 +824,7 @@ class CourseFields(object):
         scope=Scope.settings
     )
 
-    teams_configuration = Dict(
+    teams_configuration = TeamsConfigField(
         display_name=_("Teams Configuration"),
         # Translators: please don't translate "id".
         help=_(
@@ -808,6 +835,8 @@ class CourseFields(object):
             'For example, to specify that teams should have a maximum of 5 participants and provide a list of '
             '2 topics, enter the configuration in this format: {example_format}. '
             'In "id" values, the only supported special characters are underscore, hyphen, and period.'
+            # Note that we also support space (" "), which may have been an accident, but it's in
+            # our DB now. Let's not advertise the fact, though.
         ),
         help_format_args=dict(
             # Put the sample JSON into a format variable so that translators
@@ -1471,65 +1500,32 @@ class CourseDescriptor(CourseFields, SequenceDescriptor, LicenseMixin):
         """
         return course_metadata_utils.clean_course_key(self.location.course_key, padding_char)
 
-    @property
-    def teams_conf(self):
-        """
-        Returns a TeamsConfig object wrapping the dict `teams_configuration`.
-
-        TODO: In MST-18, `teams_configuration` will be a custom field that
-        parses its input into a TeamsConfig object.
-        All references to this property will become references to
-        `.teams_configuration`.
-        """
-        # If the `teams_configuration` dict hasn't changed, return a cached
-        # `TeamsConfig` to avoid re-parsing things.
-        # If it has changed, recompute the `TeamsConfig`.
-        try:
-            cached_teams_conf, cached_teams_conf_source = (
-                self._teams_conf, self._teams_conf_source
-            )
-        except AttributeError:
-            pass
-        else:
-            if cached_teams_conf_source == self.teams_configuration:
-                return cached_teams_conf
-        self._teams_conf_source = self.teams_configuration
-        self._teams_conf = TeamsConfig(self._teams_conf_source)
-        return self._teams_conf
-
     @property
     def teams_enabled(self):
         """
-        Returns whether or not teams has been enabled for this course.
+        Alias to `self.teams_configuration.is_enabled`, for convenience.
 
-        Currently, teams are considered enabled when at least one topic has been configured for the course.
-
-        Deprecated; please use `self.teams_conf.is_enabled` instead.
-        Will be removed (TODO MST-18).
+        Returns bool.
         """
-        if self.teams_configuration:
-            return len(self.teams_configuration.get('topics', [])) > 0
-        return False
+        return self.teams_configuration.is_enabled  # pylint: disable=no-member
 
     @property
-    def teams_max_size(self):
+    def teamsets(self):
         """
-        Returns the max size for teams if teams has been configured, else None.
+        Alias to `self.teams_configuration.teamsets`, for convenience.
 
-        Deprecated; please use `self.teams_conf.calc_max_team_size(...)` instead.
-        Will be removed (TODO MST-18).
+        Returns list[TeamsetConfig].
         """
-        return self.teams_configuration.get('max_team_size', None)
+        return self.teams_configuration.teamsets  # pylint: disable=no-member
 
     @property
-    def teams_topics(self):
+    def teamsets_by_id(self):
         """
-        Returns the topics that have been configured for teams for this course, else None.
+        Alias to `self.teams_configuration.teamsets_by_id`, for convenience.
 
-        Deprecated; please use `self.teams_conf.teamsets` instead.
-        Will be removed (TODO MST-18).
+        Returns dict[str: TeamsetConfig].
         """
-        return self.teams_configuration.get('topics', None)
+        return self.teams_configuration.teamsets_by_id
 
     def set_user_partitions_for_scheme(self, partitions, scheme):
         """
diff --git a/common/lib/xmodule/xmodule/tests/test_course_module.py b/common/lib/xmodule/xmodule/tests/test_course_module.py
index 0c9091f1b4..76d63be5ea 100644
--- a/common/lib/xmodule/xmodule/tests/test_course_module.py
+++ b/common/lib/xmodule/xmodule/tests/test_course_module.py
@@ -15,6 +15,7 @@ from opaque_keys.edx.keys import CourseKey
 from pytz import utc
 from xblock.runtime import DictKeyValueStore, KvsFieldData
 
+from openedx.core.lib.teams_config import TeamsConfig
 import xmodule.course_module
 from xmodule.modulestore.xml import ImportSystem, XMLModuleStore
 
@@ -272,25 +273,21 @@ class DiscussionTopicsTestCase(unittest.TestCase):
 class TeamsConfigurationTestCase(unittest.TestCase):
     """
     Tests for the configuration of teams and the helper methods for accessing them.
-
-    Also tests new configuration wrapper, `.teams_conf`.
-    Eventually the tests for the old dict-based `.teams_configuration` field
-    wil be removed (TODO MST-18).
     """
 
     def setUp(self):
         super(TeamsConfigurationTestCase, self).setUp()
         self.course = get_dummy_course('2012-12-02T12:00')
-        self.course.teams_configuration = dict()
+        self.course.teams_configuration = TeamsConfig(None)
         self.count = itertools.count()
 
     def add_team_configuration(self, max_team_size=3, topics=None):
         """ Add a team configuration to the course. """
-        teams_configuration = {}
-        teams_configuration["topics"] = [] if topics is None else topics
+        teams_config_data = {}
+        teams_config_data["topics"] = [] if topics is None else topics
         if max_team_size is not None:
-            teams_configuration["max_team_size"] = max_team_size
-        self.course.teams_configuration = teams_configuration
+            teams_config_data["max_team_size"] = max_team_size
+        self.course.teams_configuration = TeamsConfig(teams_config_data)
 
     def make_topic(self):
         """ Make a sample topic dictionary. """
@@ -303,66 +300,56 @@ class TeamsConfigurationTestCase(unittest.TestCase):
     def test_teams_enabled_new_course(self):
         # Make sure we can detect when no teams exist.
         self.assertFalse(self.course.teams_enabled)
-        self.assertFalse(self.course.teams_conf.is_enabled)
 
         # add topics
         self.add_team_configuration(max_team_size=4, topics=[self.make_topic()])
         self.assertTrue(self.course.teams_enabled)
-        self.assertTrue(self.course.teams_conf.is_enabled)
 
         # remove them again
         self.add_team_configuration(max_team_size=4, topics=[])
         self.assertFalse(self.course.teams_enabled)
-        self.assertFalse(self.course.teams_conf.is_enabled)
 
     def test_teams_enabled_max_size_only(self):
         self.add_team_configuration(max_team_size=4)
         self.assertFalse(self.course.teams_enabled)
-        self.assertFalse(self.course.teams_conf.is_enabled)
 
     def test_teams_enabled_no_max_size(self):
         self.add_team_configuration(max_team_size=None, topics=[self.make_topic()])
         self.assertTrue(self.course.teams_enabled)
-        self.assertTrue(self.course.teams_conf.is_enabled)
 
     def test_teams_max_size_no_teams_configuration(self):
-        self.assertIsNone(self.course.teams_max_size)
-        self.assertIsNone(self.course.teams_conf.max_team_size)
+        self.assertIsNone(self.course.teams_configuration.default_max_team_size)
 
     def test_teams_max_size_with_teams_configured(self):
         size = 4
         self.add_team_configuration(max_team_size=size, topics=[self.make_topic(), self.make_topic()])
         self.assertTrue(self.course.teams_enabled)
-        self.assertEqual(size, self.course.teams_max_size)
-        self.assertEqual(size, self.course.teams_conf.max_team_size)
+        self.assertEqual(size, self.course.teams_configuration.default_max_team_size)
 
-    def test_teams_topics_no_teams(self):
-        self.assertIsNone(self.course.teams_topics)
-        self.assertEqual(self.course.teams_conf.teamsets, [])
+    def test_teamsets_no_config(self):
+        self.assertEqual(self.course.teamsets, [])
 
-    def test_teams_topics_no_topics(self):
+    def test_teamsets_empty(self):
         self.add_team_configuration(max_team_size=4)
-        self.assertEqual(self.course.teams_topics, [])
-        self.assertEqual(self.course.teams_conf.teamsets, [])
+        self.assertEqual(self.course.teamsets, [])
 
-    def test_teams_topics_with_topics(self):
+    def test_teamsets_present(self):
         topics = [self.make_topic(), self.make_topic()]
         self.add_team_configuration(max_team_size=4, topics=topics)
         self.assertTrue(self.course.teams_enabled)
-        self.assertEqual(self.course.teams_topics, topics)
         expected_teamsets_data = [
             teamset.cleaned_data_old_format
-            for teamset in self.course.teams_conf.teamsets
+            for teamset in self.course.teamsets
         ]
         self.assertEqual(expected_teamsets_data, topics)
 
-    def test_teams_conf_caching(self):
+    def test_teams_conf_cached_by_xblock_field(self):
         self.add_team_configuration(max_team_size=5, topics=[self.make_topic()])
-        cold_cache_conf = self.course.teams_conf
-        warm_cache_conf = self.course.teams_conf
+        cold_cache_conf = self.course.teams_configuration
+        warm_cache_conf = self.course.teams_configuration
         self.add_team_configuration(max_team_size=5, topics=[self.make_topic(), self.make_topic()])
-        new_cold_cache_conf = self.course.teams_conf
-        new_warm_cache_conf = self.course.teams_conf
+        new_cold_cache_conf = self.course.teams_configuration
+        new_warm_cache_conf = self.course.teams_configuration
         self.assertIs(cold_cache_conf, warm_cache_conf)
         self.assertIs(new_cold_cache_conf, new_warm_cache_conf)
         self.assertIsNot(cold_cache_conf, new_cold_cache_conf)
diff --git a/common/test/acceptance/tests/lms/test_teams.py b/common/test/acceptance/tests/lms/test_teams.py
index 29c9546765..f9ab1cdff9 100644
--- a/common/test/acceptance/tests/lms/test_teams.py
+++ b/common/test/acceptance/tests/lms/test_teams.py
@@ -103,15 +103,15 @@ class TeamsTabBase(EventsTestMixin, ForumsConfigMixin, UniqueCourseTest):
         )
         return json.loads(response.text)
 
-    def set_team_configuration(self, configuration, enroll_in_course=True, global_staff=False):
+    def set_team_configuration(self, configuration_data, enroll_in_course=True, global_staff=False):
         """
         Sets team configuration on the course and calls auto-auth on the user.
         """
         #pylint: disable=attribute-defined-outside-init
         self.course_fixture = CourseFixture(**self.course_info)
-        if configuration:
+        if configuration_data:
             self.course_fixture.add_advanced_settings(
-                {u"teams_configuration": {u"value": configuration}}
+                {u"teams_configuration": {u"value": configuration_data}}
             )
         self.course_fixture.install()
 
@@ -534,7 +534,12 @@ class BrowseTopicsTest(TeamsTabBase):
         """
         initial_description = "A" + " really" * 50 + " long description"
         self.set_team_configuration(
-            {u"max_team_size": 1, u"topics": [{"name": "", "id": "", "description": initial_description}]}
+            {
+                u"max_team_size": 1,
+                u"topics": [
+                    {"id": "long-description-topic", "description": initial_description},
+                ]
+            }
         )
         self.topics_page.visit()
         truncated_description = self.topics_page.topic_descriptions[0]
diff --git a/lms/djangoapps/discussion/django_comment_client/base/tests.py b/lms/djangoapps/discussion/django_comment_client/base/tests.py
index a22bb2c73f..a4f6737cea 100644
--- a/lms/djangoapps/discussion/django_comment_client/base/tests.py
+++ b/lms/djangoapps/discussion/django_comment_client/base/tests.py
@@ -47,6 +47,7 @@ from openedx.core.djangoapps.django_comment_common.utils import (
     set_course_discussion_settings
 )
 from openedx.core.djangoapps.waffle_utils.testutils import WAFFLE_TABLES
+from openedx.core.lib.teams_config import TeamsConfig
 from student.roles import CourseStaffRole, UserBasedRole
 from student.tests.factories import CourseAccessRoleFactory, CourseEnrollmentFactory, UserFactory
 from track.middleware import TrackMiddleware
@@ -1440,10 +1441,10 @@ class TeamsPermissionsTestCase(ForumsEnableMixin, UrlResetMixin, SharedModuleSto
     def setUpClass(cls):
         # pylint: disable=super-method-not-called
         with super(TeamsPermissionsTestCase, cls).setUpClassAndTestData():
-            teams_configuration = {
+            teams_config_data = {
                 'topics': [{'id': "topic_id", 'name': 'Solar Power', 'description': 'Solar power is hot'}]
             }
-            cls.course = CourseFactory.create(teams_configuration=teams_configuration)
+            cls.course = CourseFactory.create(teams_configuration=TeamsConfig(teams_config_data))
 
     @classmethod
     def setUpTestData(cls):
diff --git a/lms/djangoapps/instructor/tests/test_api.py b/lms/djangoapps/instructor/tests/test_api.py
index 81f575ae34..4b54ed2e24 100644
--- a/lms/djangoapps/instructor/tests/test_api.py
+++ b/lms/djangoapps/instructor/tests/test_api.py
@@ -67,6 +67,7 @@ from openedx.core.djangoapps.django_comment_common.models import FORUM_ROLE_COMM
 from openedx.core.djangoapps.django_comment_common.utils import seed_permissions_roles
 from openedx.core.djangoapps.site_configuration import helpers as configuration_helpers
 from openedx.core.djangoapps.site_configuration.tests.mixins import SiteMixin
+from openedx.core.lib.teams_config import TeamsConfig
 from openedx.core.lib.xblock_utils import grade_histogram
 from shoppingcart.models import (
     Coupon,
@@ -3033,9 +3034,9 @@ class TestInstructorAPILevelsDataDump(SharedModuleStoreTestCase, LoginEnrollment
         has teams enabled, and does not when the course does not have teams enabled
         """
         if has_teams:
-            self.course = CourseFactory.create(teams_configuration={
-                'max_size': 2, 'topics': [{'topic-id': 'topic', 'name': 'Topic', 'description': 'A Topic'}]
-            })
+            self.course = CourseFactory.create(teams_configuration=TeamsConfig({
+                'max_size': 2, 'topics': [{'id': 'topic', 'name': 'Topic', 'description': 'A Topic'}]
+            }))
             course_instructor = InstructorFactory(course_key=self.course.id)
             self.client.login(username=course_instructor.username, password='test')
 
diff --git a/lms/djangoapps/instructor_task/tests/test_tasks_helper.py b/lms/djangoapps/instructor_task/tests/test_tasks_helper.py
index a5b2106dc1..ea8bc75638 100644
--- a/lms/djangoapps/instructor_task/tests/test_tasks_helper.py
+++ b/lms/djangoapps/instructor_task/tests/test_tasks_helper.py
@@ -75,6 +75,7 @@ from openedx.core.djangoapps.course_groups.tests.helpers import CohortFactory
 from openedx.core.djangoapps.credit.tests.factories import CreditCourseFactory
 from openedx.core.djangoapps.user_api.partition_schemes import RandomUserPartitionScheme
 from openedx.core.djangoapps.util.testing import ContentGroupTestCase, TestConditionalContent
+from openedx.core.lib.teams_config import TeamsConfig
 from shoppingcart.models import (
     Coupon,
     CourseRegistrationCode,
@@ -96,6 +97,12 @@ from ..models import ReportStore
 from ..tasks_helper.utils import UPDATE_STATUS_FAILED, UPDATE_STATUS_SUCCEEDED
 
 
+_TEAMS_CONFIG = TeamsConfig({
+    'max_size': 2,
+    'topics': [{'id': 'topic', 'name': 'Topic', 'description': 'A Topic'}],
+})
+
+
 class InstructorGradeReportTestCase(TestReportMixin, InstructorTaskCourseTestCase):
     """ Base class for grade report tests. """
 
@@ -403,9 +410,7 @@ class TestInstructorGradeReport(InstructorGradeReportTestCase):
             course = CourseFactory.create(
                 cohort_config={'cohorted': True, 'auto_cohort': True, 'auto_cohort_groups': ['cohort 1', 'cohort 2']},
                 user_partitions=[experiment_partition],
-                teams_configuration={
-                    'max_size': 2, 'topics': [{'topic-id': 'topic', 'name': 'Topic', 'description': 'A Topic'}]
-                },
+                teams_configuration=_TEAMS_CONFIG,
             )
         _ = CreditCourseFactory(course_key=course.id)
 
@@ -451,9 +456,7 @@ class TestTeamGradeReport(InstructorGradeReportTestCase):
 
     def setUp(self):
         super(TestTeamGradeReport, self).setUp()
-        self.course = CourseFactory.create(teams_configuration={
-            'max_size': 2, 'topics': [{'topic-id': 'topic', 'name': 'Topic', 'description': 'A Topic'}]
-        })
+        self.course = CourseFactory.create(teams_configuration=_TEAMS_CONFIG)
         self.student1 = UserFactory.create()
         CourseEnrollment.enroll(self.student1, self.course.id)
         self.student2 = UserFactory.create()
@@ -1547,9 +1550,7 @@ class TestTeamStudentReport(TestReportMixin, InstructorTaskCourseTestCase):
 
     def setUp(self):
         super(TestTeamStudentReport, self).setUp()
-        self.course = CourseFactory.create(teams_configuration={
-            'max_size': 2, 'topics': [{'topic-id': 'topic', 'name': 'Topic', 'description': 'A Topic'}]
-        })
+        self.course = CourseFactory.create(teams_configuration=_TEAMS_CONFIG)
         self.student1 = UserFactory.create()
         CourseEnrollment.enroll(self.student1, self.course.id)
         self.student2 = UserFactory.create()
diff --git a/lms/djangoapps/teams/templates/teams/teams.html b/lms/djangoapps/teams/templates/teams/teams.html
index 5b0a885a75..14278bc042 100644
--- a/lms/djangoapps/teams/templates/teams/teams.html
+++ b/lms/djangoapps/teams/templates/teams/teams.html
@@ -51,7 +51,7 @@ from openedx.core.djangolib.js_utils import (
         teamMembershipsUrl: '${team_memberships_url | n, js_escaped_string}',
         teamMembershipDetailUrl: '${team_membership_detail_url | n, js_escaped_string}',
         myTeamsUrl: '${my_teams_url | n, js_escaped_string}',
-        maxTeamSize: ${course.teams_max_size | n, dump_js_escaped_json},
+        maxTeamSize: ${course.teams_configuration.default_max_team_size | n, dump_js_escaped_json},
         languages: ${languages | n, dump_js_escaped_json},
         countries: ${countries | n, dump_js_escaped_json},
         teamsBaseUrl: '${teams_base_url | n, js_escaped_string}'
diff --git a/lms/djangoapps/teams/tests/test_serializers.py b/lms/djangoapps/teams/tests/test_serializers.py
index 3a965bdf4d..27ee6445ef 100644
--- a/lms/djangoapps/teams/tests/test_serializers.py
+++ b/lms/djangoapps/teams/tests/test_serializers.py
@@ -10,6 +10,7 @@ from django.test.client import RequestFactory
 
 from lms.djangoapps.teams.serializers import BulkTeamCountTopicSerializer, MembershipSerializer, TopicSerializer
 from lms.djangoapps.teams.tests.factories import CourseTeamFactory, CourseTeamMembershipFactory
+from openedx.core.lib.teams_config import TeamsConfig
 from student.tests.factories import CourseEnrollmentFactory, UserFactory
 from xmodule.modulestore.tests.django_utils import SharedModuleStoreTestCase
 from xmodule.modulestore.tests.factories import CourseFactory
@@ -25,10 +26,10 @@ class SerializerTestCase(SharedModuleStoreTestCase):
         """
         super(SerializerTestCase, self).setUp()
         self.course = CourseFactory.create(
-            teams_configuration={
+            teams_configuration=TeamsConfig({
                 "max_team_size": 10,
                 "topics": [{u'name': u'Tøpic', u'description': u'The bést topic!', u'id': u'0'}]
-            }
+            }),
         )
 
 
@@ -41,7 +42,7 @@ class MembershipSerializerTestCase(SerializerTestCase):
         super(MembershipSerializerTestCase, self).setUp()
         self.team = CourseTeamFactory.create(
             course_id=self.course.id,
-            topic_id=self.course.teams_topics[0]['id']
+            topic_id=self.course.teamsets[0].teamset_id,
         )
         self.user = UserFactory.create()
         CourseEnrollmentFactory.create(user=self.user, course_id=self.course.id)
@@ -81,7 +82,10 @@ class TopicSerializerTestCase(SerializerTestCase):
         team count of 0, and that it only takes one SQL query.
         """
         with self.assertNumQueries(1):
-            serializer = TopicSerializer(self.course.teams_topics[0], context={'course_id': self.course.id})
+            serializer = TopicSerializer(
+                self.course.teamsets[0].cleaned_data_old_format,
+                context={'course_id': self.course.id},
+            )
             self.assertEqual(
                 serializer.data,
                 {u'name': u'Tøpic', u'description': u'The bést topic!', u'id': u'0', u'team_count': 0}
@@ -92,9 +96,14 @@ class TopicSerializerTestCase(SerializerTestCase):
         Verifies that the `TopicSerializer` correctly displays a topic with a
         positive team count, and that it only takes one SQL query.
         """
-        CourseTeamFactory.create(course_id=self.course.id, topic_id=self.course.teams_topics[0]['id'])
+        CourseTeamFactory.create(
+            course_id=self.course.id, topic_id=self.course.teamsets[0].teamset_id
+        )
         with self.assertNumQueries(1):
-            serializer = TopicSerializer(self.course.teams_topics[0], context={'course_id': self.course.id})
+            serializer = TopicSerializer(
+                self.course.teamsets[0].cleaned_data_old_format,
+                context={'course_id': self.course.id},
+            )
             self.assertEqual(
                 serializer.data,
                 {u'name': u'Tøpic', u'description': u'The bést topic!', u'id': u'0', u'team_count': 1}
@@ -102,17 +111,20 @@ class TopicSerializerTestCase(SerializerTestCase):
 
     def test_scoped_within_course(self):
         """Verify that team count is scoped within a course."""
-        duplicate_topic = self.course.teams_topics[0]
+        duplicate_topic = self.course.teamsets[0].cleaned_data_old_format
         second_course = CourseFactory.create(
-            teams_configuration={
+            teams_configuration=TeamsConfig({
                 "max_team_size": 10,
                 "topics": [duplicate_topic]
-            }
+            }),
         )
         CourseTeamFactory.create(course_id=self.course.id, topic_id=duplicate_topic[u'id'])
         CourseTeamFactory.create(course_id=second_course.id, topic_id=duplicate_topic[u'id'])
         with self.assertNumQueries(1):
-            serializer = TopicSerializer(self.course.teams_topics[0], context={'course_id': self.course.id})
+            serializer = TopicSerializer(
+                self.course.teamsets[0].cleaned_data_old_format,
+                context={'course_id': self.course.id},
+            )
             self.assertEqual(
                 serializer.data,
                 {u'name': u'Tøpic', u'description': u'The bést topic!', u'id': u'0', u'team_count': 1}
@@ -140,16 +152,17 @@ class BaseTopicSerializerTestCase(SerializerTestCase):
         Helper method to set up topics on the course.  Returns a list of
         created topics.
         """
-        self.course.teams_configuration['topics'] = []
         topics = [
             {u'name': u'Tøpic {}'.format(i), u'description': u'The bést topic! {}'.format(i), u'id': six.text_type(i)}
             for i in six.moves.range(num_topics)
         ]
-        for i in six.moves.range(num_topics):
-            topic_id = six.text_type(i)
-            self.course.teams_configuration['topics'].append(topics[i])
+        for topic in topics:
             for _ in six.moves.range(teams_per_topic):
-                CourseTeamFactory.create(course_id=self.course.id, topic_id=topic_id)
+                CourseTeamFactory.create(course_id=self.course.id, topic_id=topic['id'])
+        self.course.teams_configuration = TeamsConfig({
+            'max_team_size': self.course.teams_configuration.default_max_team_size,
+            'topics': topics,
+        })
         return topics
 
     def assert_serializer_output(self, topics, num_teams_per_topic, num_queries):
@@ -157,7 +170,10 @@ class BaseTopicSerializerTestCase(SerializerTestCase):
         Verify that the serializer produced the expected topics.
         """
         with self.assertNumQueries(num_queries):
-            page = Paginator(self.course.teams_topics, self.PAGE_SIZE).page(1)
+            page = Paginator(
+                self.course.teams_configuration.cleaned_data_old_format['topics'],
+                self.PAGE_SIZE,
+            ).page(1)
             # pylint: disable=not-callable
             serializer = self.serializer(instance=page, context={'course_id': self.course.id})
             self.assertEqual(
@@ -170,7 +186,7 @@ class BaseTopicSerializerTestCase(SerializerTestCase):
         Verify that we return no results and make no SQL queries for a page
         with no topics.
         """
-        self.course.teams_configuration['topics'] = []
+        self.course.teams_configuration = TeamsConfig({'topics': []})
         self.assert_serializer_output([], num_teams_per_topic=0, num_queries=0)
 
 
@@ -216,10 +232,10 @@ class BulkTeamCountTopicSerializerTestCase(BaseTopicSerializerTestCase):
         first_course_topics = self.setup_topics(num_topics=self.NUM_TOPICS, teams_per_topic=teams_per_topic)
         duplicate_topic = first_course_topics[0]
         second_course = CourseFactory.create(
-            teams_configuration={
+            teams_configuration=TeamsConfig({
                 "max_team_size": 10,
                 "topics": [duplicate_topic]
-            }
+            }),
         )
         CourseTeamFactory.create(course_id=second_course.id, topic_id=duplicate_topic[u'id'])
         self.assert_serializer_output(first_course_topics, num_teams_per_topic=teams_per_topic, num_queries=1)
@@ -230,23 +246,6 @@ class BulkTeamCountTopicSerializerTestCase(BaseTopicSerializerTestCase):
         result.update(second)
         return result
 
-    def setup_topics(self, num_topics=5, teams_per_topic=0):
-        """
-        Helper method to set up topics on the course.  Returns a list of
-        created topics.
-        """
-        self.course.teams_configuration['topics'] = []
-        topics = [
-            {u'name': u'Tøpic {}'.format(i), u'description': u'The bést topic! {}'.format(i), u'id': six.text_type(i)}
-            for i in six.moves.range(num_topics)
-        ]
-        for i in six.moves.range(num_topics):
-            topic_id = six.text_type(i)
-            self.course.teams_configuration['topics'].append(topics[i])
-            for _ in six.moves.range(teams_per_topic):
-                CourseTeamFactory.create(course_id=self.course.id, topic_id=topic_id)
-        return topics
-
     def assert_serializer_output(self, topics, num_teams_per_topic, num_queries):
         """
         Verify that the serializer produced the expected topics.
@@ -263,5 +262,5 @@ class BulkTeamCountTopicSerializerTestCase(BaseTopicSerializerTestCase):
         Verify that we return no results and make no SQL queries for a page
         with no topics.
         """
-        self.course.teams_configuration['topics'] = []
+        self.course.teams_configuration = TeamsConfig({'topics': []})
         self.assert_serializer_output([], num_teams_per_topic=0, num_queries=0)
diff --git a/lms/djangoapps/teams/tests/test_views.py b/lms/djangoapps/teams/tests/test_views.py
index 4d4d938d7e..5d6ec0300f 100644
--- a/lms/djangoapps/teams/tests/test_views.py
+++ b/lms/djangoapps/teams/tests/test_views.py
@@ -25,6 +25,7 @@ from common.test.utils import skip_signal
 from lms.djangoapps.courseware.tests.factories import StaffFactory
 from openedx.core.djangoapps.django_comment_common.models import FORUM_ROLE_COMMUNITY_TA, Role
 from openedx.core.djangoapps.django_comment_common.utils import seed_permissions_roles
+from openedx.core.lib.teams_config import TeamsConfig
 from student.models import CourseEnrollment
 from student.tests.factories import AdminFactory, CourseEnrollmentFactory, UserFactory
 from util.testing import EventTestMixin
@@ -46,7 +47,7 @@ class TestDashboard(SharedModuleStoreTestCase):
     def setUpClass(cls):
         super(TestDashboard, cls).setUpClass()
         cls.course = CourseFactory.create(
-            teams_configuration={
+            teams_configuration=TeamsConfig({
                 "max_team_size": 10,
                 "topics": [
                     {
@@ -56,7 +57,7 @@ class TestDashboard(SharedModuleStoreTestCase):
                     }
                     for topic_id in range(cls.NUM_TOPICS)
                 ]
-            }
+            })
         )
 
     def setUp(self):
@@ -158,7 +159,7 @@ class TestDashboard(SharedModuleStoreTestCase):
 
         # Create a course two
         course_two = CourseFactory.create(
-            teams_configuration={
+            teams_configuration=TeamsConfig({
                 "max_team_size": 1,
                 "topics": [
                     {
@@ -167,7 +168,7 @@ class TestDashboard(SharedModuleStoreTestCase):
                         "description": "Description for test topic for course two."
                     }
                 ]
-            }
+            })
         )
 
         # Login and enroll user in both course course
@@ -204,7 +205,7 @@ class TeamAPITestCase(APITestCase, SharedModuleStoreTestCase):
     def setUpClass(cls):
         # pylint: disable=super-method-not-called
         with super(TeamAPITestCase, cls).setUpClassAndTestData():
-            teams_configuration_1 = {
+            teams_configuration_1 = TeamsConfig({
                 'topics':
                 [
                     {
@@ -213,7 +214,7 @@ class TeamAPITestCase(APITestCase, SharedModuleStoreTestCase):
                         'description': u'Description for topic {}.'.format(i)
                     } for i, name in enumerate([u'Sólar power', 'Wind Power', 'Nuclear Power', 'Coal Power'])
                 ]
-            }
+            })
             cls.test_course_1 = CourseFactory.create(
                 org='TestX',
                 course='TS101',
@@ -221,7 +222,7 @@ class TeamAPITestCase(APITestCase, SharedModuleStoreTestCase):
                 teams_configuration=teams_configuration_1
             )
 
-            teams_configuration_2 = {
+            teams_configuration_2 = TeamsConfig({
                 'topics':
                 [
                     {
@@ -241,7 +242,7 @@ class TeamAPITestCase(APITestCase, SharedModuleStoreTestCase):
                     },
                 ],
                 'max_team_size': 1
-            }
+            })
             cls.test_course_2 = CourseFactory.create(
                 org='MIT',
                 course='6.002x',
diff --git a/lms/djangoapps/teams/views.py b/lms/djangoapps/teams/views.py
index b6f270d825..4c329a5d05 100644
--- a/lms/djangoapps/teams/views.py
+++ b/lms/djangoapps/teams/views.py
@@ -404,7 +404,7 @@ class TeamsListView(ExpandableFieldViewMixin, GenericAPIView):
             result_filter.update({'membership__user__username': username})
         topic_id = request.query_params.get('topic_id', None)
         if topic_id is not None:
-            if topic_id not in [topic['id'] for topic in course_module.teams_configuration['topics']]:
+            if topic_id not in course_module.teamsets_by_id:
                 error = build_api_error(
                     ugettext_noop(u'The supplied topic id {topic_id} is not valid'),
                     topic_id=topic_id
@@ -824,7 +824,10 @@ def get_alphabetical_topics(course_module):
     Returns:
         list: a list of sorted team topics
     """
-    return sorted(course_module.teams_topics, key=lambda t: t['name'].lower())
+    return sorted(
+        course_module.teams_configuration.cleaned_data_old_format['topics'],
+        key=lambda t: t['name'].lower(),
+    )
 
 
 class TopicDetailView(APIView):
@@ -884,12 +887,14 @@ class TopicDetailView(APIView):
         if not has_team_api_access(request.user, course_id):
             return Response(status=status.HTTP_403_FORBIDDEN)
 
-        topics = [t for t in course_module.teams_topics if t['id'] == topic_id]
-
-        if not topics:
+        try:
+            topic = course_module.teamsets_by_id[topic_id]
+        except KeyError:
             return Response(status=status.HTTP_404_NOT_FOUND)
 
-        serializer = TopicSerializer(topics[0], context={'course_id': course_id})
+        serializer = TopicSerializer(
+            topic.cleaned_data_old_format, context={'course_id': course_id}
+        )
         return Response(serializer.data)
 
 
@@ -1112,7 +1117,9 @@ class MembershipListView(ExpandableFieldViewMixin, GenericAPIView):
             return Response(status=status.HTTP_404_NOT_FOUND)
 
         course_module = modulestore().get_course(team.course_id)
-        if course_module.teams_max_size is not None and team.users.count() >= course_module.teams_max_size:
+        # This should use `calc_max_team_size` instead of `default_max_team_size` (TODO MST-32).
+        max_team_size = course_module.teams_configuration.default_max_team_size
+        if max_team_size is not None and team.users.count() >= max_team_size:
             return Response(
                 build_api_error(ugettext_noop("This team is already full.")),
                 status=status.HTTP_400_BAD_REQUEST
diff --git a/openedx/core/lib/teams_config.py b/openedx/core/lib/teams_config.py
index 7f0b9a816f..4257153701 100644
--- a/openedx/core/lib/teams_config.py
+++ b/openedx/core/lib/teams_config.py
@@ -41,12 +41,25 @@ class TeamsConfig(object):
         """
         Return developer-helpful string.
         """
-        return "<{} max_team_size={} teamsets=[{}]>".format(
+        return "<{} default_max_team_size={} teamsets=[{}]>".format(
             self.__class__.__name__,
-            self.max_team_size,
+            self.default_max_team_size,
             ", ".join(repr(teamset) for teamset in self.teamsets),
         )
 
+    def __eq__(self, other):
+        """
+        Define equality based on cleaned data.
+        """
+        return isinstance(other, self.__class__) and self.cleaned_data == other.cleaned_data
+
+    def __ne__(self, other):
+        """
+        Overrides default inequality to be the inverse of our custom equality.
+        Safe to remove once we're in Python 3 -- Py3 does this for us.
+        """
+        return not self.__eq__(other)
+
     @property
     def source_data(self):
         """
@@ -60,7 +73,7 @@ class TeamsConfig(object):
         JSON-friendly dictionary containing cleaned data from this TeamsConfig.
         """
         return {
-            'max_team_size': self.max_team_size,
+            'max_team_size': self.default_max_team_size,
             'team_sets': [
                 teamset.cleaned_data for teamset in self.teamsets
             ]
@@ -72,10 +85,10 @@ class TeamsConfig(object):
         JSON-friendly dictionary containing cleaned data from this TeamsConfig,
         excluding newly added fields.
 
-        Here for backwards compatibility; to be removed (TODO MST-18).
+        Here for backwards compatibility; to be removed (TODO MST-40).
         """
         return {
-            'max_team_size': self.max_team_size,
+            'max_team_size': self.default_max_team_size,
             'topics': [
                 teamset.cleaned_data_old_format for teamset in self.teamsets
             ]
@@ -123,9 +136,11 @@ class TeamsConfig(object):
         return {teamset.teamset_id: teamset for teamset in self.teamsets}
 
     @cached_property
-    def max_team_size(self):
+    def default_max_team_size(self):
         """
         The default maximum size for teams in this course.
+
+        Can be overriden by individual team sets; see `calc_max_team_size`.
         """
         return _clean_max_team_size(self._data.get('max_team_size'))
 
@@ -147,7 +162,7 @@ class TeamsConfig(object):
             return None
         if teamset.max_team_size:
             return teamset.max_team_size
-        return self.max_team_size
+        return self.default_max_team_size
 
 
 class TeamsetConfig(object):
@@ -157,7 +172,7 @@ class TeamsetConfig(object):
     Takes in a configuration from a JSON-friendly dictionary,
     and exposes cleaned data from it.
     """
-    teamset_id_regex = re.compile(r'^[A-Za-z0-9_-]+$')
+    teamset_id_regex = re.compile(r'^[A-Za-z0-9_. -]+$')
 
     def __init__(self, data):
         """
@@ -192,6 +207,19 @@ class TeamsetConfig(object):
             ),
         )
 
+    def __eq__(self, other):
+        """
+        Define equality based on cleaned data.
+        """
+        return isinstance(other, self.__class__) and self.cleaned_data == other.cleaned_data
+
+    def __ne__(self, other):
+        """
+        Overrides default inequality to be the inverse of our custom equality.
+        Safe to remove once we're in Python 3 -- Py3 does this for us.
+        """
+        return not self.__eq__(other)
+
     @property
     def source_data(self):
         """
@@ -218,7 +246,7 @@ class TeamsetConfig(object):
         JSON-friendly dictionary containing cleaned data from this TeamsConfig,
         excluding newly added fields.
 
-        Here for backwards compatibility; to be removed (TODO MST-18).
+        Here for backwards compatibility; to be removed (TODO MST-40).
         """
         return {
             'id': self.teamset_id,
@@ -231,7 +259,8 @@ class TeamsetConfig(object):
         """
         An identifier for this team-set.
 
-        Should be a URL-slug friendly string.
+        Should be a URL-slug friendly string,
+        but for a historical reasons may contain periods and spaces.
         """
         teamset_id = _clean_string(self._data.get('id'))
         if not self.teamset_id_regex.match(teamset_id):
@@ -301,11 +330,11 @@ class TeamsetType(Enum):
 
 def _clean_string(value):
     """
-    Return `value` if it's a string, otherwise "".
+    Return `str(value)` if it's a string or int, otherwise "".
     """
-    if not isinstance(value, six.string_types):
-        return ""
-    return value
+    if isinstance(value, six.integer_types + six.string_types):
+        return six.text_type(value)
+    return ""
 
 
 def _clean_max_team_size(value):
diff --git a/openedx/core/lib/tests/test_teams_config.py b/openedx/core/lib/tests/test_teams_config.py
index 8d27f9b5e1..70ce37b5c5 100644
--- a/openedx/core/lib/tests/test_teams_config.py
+++ b/openedx/core/lib/tests/test_teams_config.py
@@ -91,14 +91,14 @@ class TeamsConfigTests(TestCase):
             },
             {
                 # Team-set should be dropped due to invalid ID.
-                "id": "Not a slug.",
-                "name": "Assignment about slugs",
+                "id": "the character & cannot be in an ID",
+                "name": "Assignment about ampersands",
             },
             {
                 # All fields invalid except ID;
                 # Team-set will exist but have all fallbacks.
-                "id": "horses",
-                "name": {"assignment", "about", "horses"},
+                "id": "_1. How quickly daft-jumping zebras vex",
+                "name": {"assignment", "about", "zebras"},
                 "description": object(),
                 "max_team_size": -1000,
                 "type": "matrix",
@@ -115,8 +115,8 @@ class TeamsConfigTests(TestCase):
         "max_team_size": None,
         "team_sets": [
             {
-                "id": "horses",
-                "name": "horses",
+                "id": "_1. How quickly daft-jumping zebras vex",
+                "name": "_1. How quickly daft-jumping zebras vex",
                 "description": "",
                 "max_team_size": None,
                 "type": "open",
@@ -202,3 +202,11 @@ class TeamsConfigTests(TestCase):
         assert '987' in config_repr
         assert 'open' in config_repr
         assert 'hedgehogs' in config_repr
+
+    def test_teamset_int_id(self):
+        """
+        Assert integer teaset IDs are treated as strings,
+        for backwards compatibility.
+        """
+        teamset = TeamsetConfig({"id": 5})
+        assert teamset.teamset_id == "5"