diff --git a/common/djangoapps/student/helpers.py b/common/djangoapps/student/helpers.py
index 366d6d33d5..f123691393 100644
--- a/common/djangoapps/student/helpers.py
+++ b/common/djangoapps/student/helpers.py
@@ -11,7 +11,7 @@ from datetime import datetime
 
 import six.moves.urllib.parse
 from completion.exceptions import UnavailableCompletionData
-from completion.utilities import get_key_to_last_completed_course_block
+from completion.utilities import get_key_to_last_completed_block
 from django.conf import settings
 from django.contrib.auth import load_backend
 from django.contrib.auth.models import User
@@ -686,7 +686,7 @@ def get_resume_urls_for_enrollments(user, enrollments):
     resume_course_urls = OrderedDict()
     for enrollment in enrollments:
         try:
-            block_key = get_key_to_last_completed_course_block(user, enrollment.course_id)
+            block_key = get_key_to_last_completed_block(user, enrollment.course_id)
             url_to_block = reverse(
                 'jump_to',
                 kwargs={'course_id': enrollment.course_id, 'location': block_key}
diff --git a/common/djangoapps/student/tests/test_views.py b/common/djangoapps/student/tests/test_views.py
index fe18588917..3f956d2a7c 100644
--- a/common/djangoapps/student/tests/test_views.py
+++ b/common/djangoapps/student/tests/test_views.py
@@ -703,7 +703,7 @@ class StudentDashboardTests(SharedModuleStoreTestCase, MilestonesTestCaseMixin,
             for number in range(5)
         ]
 
-        submit_completions_for_testing(self.user, course_key, block_keys)
+        submit_completions_for_testing(self.user, block_keys)
 
         response = self.client.get(reverse('dashboard'))
 
@@ -816,7 +816,7 @@ class StudentDashboardTests(SharedModuleStoreTestCase, MilestonesTestCaseMixin,
                 ]
                 last_completed_block_string = str(block_keys[-1])
 
-                submit_completions_for_testing(self.user, course_key, block_keys)
+                submit_completions_for_testing(self.user, block_keys)
 
             html_for_view_buttons.append(
                 self._get_html_for_view_course_button(
diff --git a/lms/djangoapps/course_api/blocks/transformers/block_completion.py b/lms/djangoapps/course_api/blocks/transformers/block_completion.py
index 0c4f5a730d..a2b0be3d2a 100644
--- a/lms/djangoapps/course_api/blocks/transformers/block_completion.py
+++ b/lms/djangoapps/course_api/blocks/transformers/block_completion.py
@@ -61,7 +61,7 @@ class BlockCompletionTransformer(BlockStructureTransformer):
 
         completions = BlockCompletion.objects.filter(
             user=usage_info.user,
-            course_key=usage_info.course_key,
+            context_key=usage_info.course_key,
         ).values_list(
             'block_key',
             'completion',
diff --git a/lms/djangoapps/course_api/blocks/transformers/tests/test_block_completion.py b/lms/djangoapps/course_api/blocks/transformers/tests/test_block_completion.py
index dafdbae862..ad5fd82d8e 100644
--- a/lms/djangoapps/course_api/blocks/transformers/tests/test_block_completion.py
+++ b/lms/djangoapps/course_api/blocks/transformers/tests/test_block_completion.py
@@ -82,7 +82,6 @@ class BlockCompletionTransformerTestCase(TransformerRegistryTestMixin, Completio
         block = ItemFactory.create(category='comp', parent=course)
         BlockCompletion.objects.submit_completion(
             user=self.user,
-            course_key=block.location.course_key,
             block_key=block.location,
             completion=self.COMPLETION_TEST_VALUE,
         )
diff --git a/lms/djangoapps/courseware/module_render.py b/lms/djangoapps/courseware/module_render.py
index 36e7036661..b6ce3b34a0 100644
--- a/lms/djangoapps/courseware/module_render.py
+++ b/lms/djangoapps/courseware/module_render.py
@@ -569,7 +569,6 @@ def get_module_system_for_user(
         else:
             BlockCompletion.objects.submit_completion(
                 user=user,
-                course_key=course_id,
                 block_key=block.scope_ids.usage_id,
                 completion=event['completion'],
             )
@@ -614,7 +613,6 @@ def get_module_system_for_user(
             if not getattr(block, 'has_custom_completion', False):
                 BlockCompletion.objects.submit_completion(
                     user=user,
-                    course_key=course_id,
                     block_key=block.scope_ids.usage_id,
                     completion=1.0,
                 )
diff --git a/lms/djangoapps/gating/signals.py b/lms/djangoapps/gating/signals.py
index 0c782cf75a..00e17af2d4 100644
--- a/lms/djangoapps/gating/signals.py
+++ b/lms/djangoapps/gating/signals.py
@@ -37,7 +37,9 @@ def evaluate_subsection_completion_milestones(**kwargs):
     evaluation of any milestone which can be completed.
     """
     instance = kwargs['instance']
-    course_id = six.text_type(instance.course_key)
+    course_id = six.text_type(instance.context_key)
+    if not instance.context_key.is_course:
+        return  # Content in a library or some other thing that doesn't support milestones
     block_id = six.text_type(instance.block_key)
     user_id = instance.user_id
     task_evaluate_subsection_completion_milestones(course_id, block_id, user_id)
diff --git a/lms/djangoapps/lms_xblock/runtime.py b/lms/djangoapps/lms_xblock/runtime.py
index 8b9d68e65c..3df3c6a899 100644
--- a/lms/djangoapps/lms_xblock/runtime.py
+++ b/lms/djangoapps/lms_xblock/runtime.py
@@ -142,7 +142,7 @@ class LmsModuleSystem(ModuleSystem):  # pylint: disable=abstract-method
         services = kwargs.setdefault('services', {})
         user = kwargs.get('user')
         if user and user.is_authenticated:
-            services['completion'] = CompletionService(user=user, course_key=kwargs.get('course_id'))
+            services['completion'] = CompletionService(user=user, context_key=kwargs.get('course_id'))
         services['fs'] = xblock.reference.plugins.FSService()
         services['i18n'] = ModuleI18nService
         services['library_tools'] = LibraryToolsService(store)
diff --git a/openedx/core/djangoapps/content_libraries/tests/test_content_libraries.py b/openedx/core/djangoapps/content_libraries/tests/test_content_libraries.py
index 643bda1030..34872ec0ae 100644
--- a/openedx/core/djangoapps/content_libraries/tests/test_content_libraries.py
+++ b/openedx/core/djangoapps/content_libraries/tests/test_content_libraries.py
@@ -11,6 +11,7 @@ from organizations.models import Organization
 from rest_framework.test import APITestCase
 
 from student.tests.factories import UserFactory
+from openedx.core.djangolib.testing.utils import skip_unless_cms
 from openedx.core.lib import blockstore_api
 
 # Define the URLs here - don't use reverse() because we want to detect
@@ -29,7 +30,7 @@ URL_BLOCK_GET_HANDLER_URL = '/api/xblock/v2/xblocks/{block_key}/handler_url/{han
 
 
 @unittest.skipUnless(settings.RUN_BLOCKSTORE_TESTS, "Requires a running Blockstore server")
-@unittest.skipUnless(settings.ROOT_URLCONF == "cms.urls", "Content Libraries REST API is only available in Studio")
+@skip_unless_cms  # Content Libraries REST API is only available in Studio
 class ContentLibrariesTest(APITestCase):
     """
     Test for Blockstore-based Content Libraries
diff --git a/openedx/core/djangoapps/content_libraries/tests/test_runtime.py b/openedx/core/djangoapps/content_libraries/tests/test_runtime.py
index c863e7afa1..17dd2cb550 100644
--- a/openedx/core/djangoapps/content_libraries/tests/test_runtime.py
+++ b/openedx/core/djangoapps/content_libraries/tests/test_runtime.py
@@ -6,6 +6,7 @@ from __future__ import absolute_import, division, print_function, unicode_litera
 import json
 import unittest
 
+from completion.test_utils import CompletionWaffleTestMixin
 from django.conf import settings
 from django.test import TestCase
 from organizations.models import Organization
@@ -20,6 +21,7 @@ from openedx.core.djangoapps.content_libraries.tests.test_content_libraries impo
     URL_BLOCK_GET_HANDLER_URL,
 )
 from openedx.core.djangoapps.xblock import api as xblock_api
+from openedx.core.djangolib.testing.utils import skip_unless_lms
 from openedx.core.lib import blockstore_api
 from student.tests.factories import UserFactory
 from xmodule.unit_block import UnitBlock
@@ -93,7 +95,7 @@ class ContentLibraryRuntimeTest(ContentLibraryContentTestMixin, TestCase):
 @unittest.skipUnless(settings.RUN_BLOCKSTORE_TESTS, "Requires a running Blockstore server")
 # We can remove the line below to enable this in Studio once we implement a session-backed
 # field data store which we can use for both studio users and anonymous users
-@unittest.skipUnless(settings.ROOT_URLCONF == "lms.urls", "Student State is only saved in the LMS")
+@skip_unless_lms
 class ContentLibraryXBlockUserStateTest(ContentLibraryContentTestMixin, TestCase):
     """
     Test that the Blockstore-based XBlock runtime can store and retrieve student
@@ -195,7 +197,7 @@ class ContentLibraryXBlockUserStateTest(ContentLibraryContentTestMixin, TestCase
         # Now they should be equal, because we've saved and re-loaded instance2:
         self.assertEqual(block_instance1.user_str, block_instance2.user_str)
 
-    @unittest.skipUnless(settings.ROOT_URLCONF == "lms.urls", "Scores are only used in the LMS")
+    @skip_unless_lms  # Scores are only used in the LMS
     def test_scores_persisted(self):
         """
         Test that a block's emitted scores are cached in StudentModule
@@ -260,3 +262,58 @@ class ContentLibraryXBlockUserStateTest(ContentLibraryContentTestMixin, TestCase
         sm = get_score(self.student_a, block_id)
         self.assertEqual(sm.grade, 1)
         self.assertEqual(sm.max_grade, 1)
+
+
+@unittest.skipUnless(settings.RUN_BLOCKSTORE_TESTS, "Requires a running Blockstore server")
+@skip_unless_lms  # No completion tracking in Studio
+class ContentLibraryXBlockCompletionTest(ContentLibraryContentTestMixin, CompletionWaffleTestMixin, TestCase):
+    """
+    Test that the Blockstore-based XBlocks can track their completion status
+    using the completion library.
+    """
+
+    def setUp(self):
+        super(ContentLibraryXBlockCompletionTest, self).setUp()
+        # Enable the completion waffle flag for these tests
+        self.override_waffle_switch(True)
+
+    def test_mark_complete_via_handler(self):
+        """
+        Test that a "complete on view" XBlock like the HTML block can be marked
+        as complete using the LmsBlockMixin.publish_completion handler.
+        """
+        block_id = library_api.create_library_block(self.library.key, "html", "completable_html").usage_key
+        new_olx = """
+        <html display_name="Read this HTML">
+            <![CDATA[
+                <p>This is some <strong>HTML</strong>.</p>
+            ]]>
+        </html>
+        """.strip()
+        library_api.set_library_block_olx(block_id, new_olx)
+        library_api.publish_changes(self.library.key)
+
+        # We should get a REST API for retrieving completion data; for now use python
+
+        def get_block_completion_status():
+            """ Get block completion status (0 to 1) """
+            block = xblock_api.load_block(block_id, self.student_a)
+            assert hasattr(block, 'publish_completion')
+            service = block.runtime.service(block, 'completion')
+            return service.get_completions([block_id])[block_id]
+
+        # At first the block is not completed
+        self.assertEqual(get_block_completion_status(), 0)
+
+        # Now call the 'publish_completion' handler:
+        client = APIClient()
+        client.login(username=self.student_a.username, password='edx')
+        result = client.get(URL_BLOCK_GET_HANDLER_URL.format(block_key=block_id, handler_name='publish_completion'))
+        publish_completion_url = result.data["handler_url"]
+
+        # This will test the 'completion' service and the completion event handler:
+        result2 = client.post(publish_completion_url, {"completion": 1.0}, format='json')
+        self.assertEqual(result2.status_code, 200)
+
+        # Now the block is completed
+        self.assertEqual(get_block_completion_status(), 1)
diff --git a/openedx/core/djangoapps/user_api/accounts/tests/test_utils.py b/openedx/core/djangoapps/user_api/accounts/tests/test_utils.py
index b492c015b1..e9ce9699d7 100644
--- a/openedx/core/djangoapps/user_api/accounts/tests/test_utils.py
+++ b/openedx/core/djangoapps/user_api/accounts/tests/test_utils.py
@@ -106,7 +106,6 @@ class CompletionUtilsTestCase(SharedModuleStoreTestCase, CompletionWaffleTestMix
         for block in self.course.children[0].children[0].children:
             models.BlockCompletion.objects.submit_completion(
                 user=self.engaged_user,
-                course_key=self.course.id,
                 block_key=block.location,
                 completion=1.0
             )
diff --git a/openedx/core/djangoapps/xblock/rest_api/views.py b/openedx/core/djangoapps/xblock/rest_api/views.py
index 425ee09394..055d070fe1 100644
--- a/openedx/core/djangoapps/xblock/rest_api/views.py
+++ b/openedx/core/djangoapps/xblock/rest_api/views.py
@@ -7,6 +7,8 @@ Studio APIs cover use cases like adding/deleting/editing blocks.
 from __future__ import absolute_import, division, print_function, unicode_literals
 
 from django.contrib.auth import get_user_model
+from django.views.decorators.clickjacking import xframe_options_exempt
+from django.views.decorators.csrf import csrf_exempt
 from rest_framework import permissions
 from rest_framework.decorators import api_view, permission_classes, authentication_classes
 from rest_framework.exceptions import PermissionDenied, AuthenticationFailed
@@ -68,12 +70,19 @@ def get_handler_url(request, usage_key_str, handler_name):
     return Response({"handler_url": handler_url})
 
 
-@api_view(['GET', 'POST', 'PUT', 'PATCH', 'DELETE'])
-@authentication_classes([])  # Disable session authentication; we don't need it and don't want CSRF checks
-@permission_classes((permissions.AllowAny, ))
+# We cannot use DRF for this endpoint because its Request object is incompatible
+# with the API expected by XBlock handlers.
+# See https://github.com/edx/edx-platform/pull/19253
+# and https://github.com/edx/XBlock/pull/383 for context.
+@csrf_exempt
+@xframe_options_exempt
 def xblock_handler(request, user_id, secure_token, usage_key_str, handler_name, suffix):
     """
     Run an XBlock's handler and return the result
+
+    This endpoint has a unique authentication scheme that involves a temporary
+    auth token included in the URL (see below). As a result it can be exempt
+    from CSRF, session auth, and JWT/OAuth.
     """
     user_id = int(user_id)  # User ID comes from the URL, not session auth
     usage_key = UsageKey.from_string(usage_key_str)
diff --git a/openedx/core/djangoapps/xblock/runtime/mixin.py b/openedx/core/djangoapps/xblock/runtime/mixin.py
index 3de50b4846..52086be9b4 100644
--- a/openedx/core/djangoapps/xblock/runtime/mixin.py
+++ b/openedx/core/djangoapps/xblock/runtime/mixin.py
@@ -2,9 +2,14 @@
 A mixin that provides functionality and default attributes for all XBlocks in
 the new XBlock runtime.
 """
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+from xblock.core import XBlock, XBlockMixin
+from xblock.exceptions import JsonHandlerError
 
 
-class LmsBlockMixin(object):
+@XBlock.wants('completion')
+class LmsBlockMixin(XBlockMixin):
     """
     A mixin that provides functionality and default attributes for all XBlocks
     in the new XBlock runtime.
@@ -17,3 +22,21 @@ class LmsBlockMixin(object):
     # static content). If it does, it should set this and provide scoring
     # functionality by inheriting xblock.scorable.ScorableXBlockMixin
     has_score = False
+
+    @XBlock.json_handler
+    def publish_completion(self, data, suffix=''):  # pylint: disable=unused-argument
+        """
+        Allow the frontend app that's rendering this XBlock to mark it as
+        completed when the user views it, if appropriate.
+
+        Copied from lms.djangoapps.lms_xblock.mixin.LmsBlockMixin
+        """
+        completion_service = self.runtime.service(self, 'completion')
+        if completion_service is None:
+            raise JsonHandlerError(500, u"No completion service found")
+        elif not completion_service.completion_tracking_enabled():
+            raise JsonHandlerError(404, u"Completion tracking is not enabled and API calls are unexpected")
+        if not completion_service.can_mark_block_complete_on_view(self):
+            raise JsonHandlerError(400, u"Block not configured for completion on view.")
+        self.runtime.publish(self, "completion", data)
+        return {'result': 'ok'}
diff --git a/openedx/core/djangoapps/xblock/runtime/runtime.py b/openedx/core/djangoapps/xblock/runtime/runtime.py
index e891e9698c..b0df80894f 100644
--- a/openedx/core/djangoapps/xblock/runtime/runtime.py
+++ b/openedx/core/djangoapps/xblock/runtime/runtime.py
@@ -5,6 +5,8 @@ from __future__ import absolute_import, division, print_function, unicode_litera
 import logging
 
 from completion import waffle as completion_waffle
+from completion.models import BlockCompletion
+from completion.services import CompletionService
 import crum
 from django.contrib.auth import get_user_model
 from django.utils.lru_cache import lru_cache
@@ -131,8 +133,7 @@ class XBlockRuntime(RuntimeShim, Runtime):
         if event_type == 'grade':
             return self.handle_grade_event
         elif event_type == 'completion':
-            if completion_waffle.waffle().is_enabled(completion_waffle.ENABLE_COMPLETION_TRACKING):
-                return self.handle_completion_event
+            return self.handle_completion_event
         return None
 
     def log_event_to_tracking_log(self, block, event_type, event_data):
@@ -167,16 +168,13 @@ class XBlockRuntime(RuntimeShim, Runtime):
         """
         Submit a completion object for the block.
         """
-        block_key = block.scope_ids.usage_id
-        # edx-completion needs to be updated to support learning contexts, which is coming soon in a separate PR.
-        # For now just log a debug statement to confirm this plumbing is ready to send those events through.
-        log.debug("Completion event for block {}: new completion = {}".format(block_key, event['completion']))
-        # BlockCompletion.objects.submit_completion(
-        #     user=self.user,
-        #     course_key=block_key.context_key,
-        #     block_key=block_key,
-        #     completion=event['completion'],
-        # )
+        if not completion_waffle.waffle().is_enabled(completion_waffle.ENABLE_COMPLETION_TRACKING):
+            return
+        BlockCompletion.objects.submit_completion(
+            user=self.user,
+            block_key=block.scope_ids.usage_id,
+            completion=event['completion'],
+        )
 
     def applicable_aside_types(self, block):
         """ Disable XBlock asides in this runtime """
@@ -213,6 +211,9 @@ class XBlockRuntime(RuntimeShim, Runtime):
                     self.block_field_datas[block.scope_ids] = None
                     raise
             return self.block_field_datas[block.scope_ids]
+        elif service_name == "completion":
+            context_key = block.scope_ids.usage_id.context_key
+            return CompletionService(user=self.user, context_key=context_key)
         # Check if the XBlockRuntimeSystem wants to handle this:
         service = self.system.get_service(block, service_name)
         # Otherwise, fall back to the base implementation which loads services
diff --git a/openedx/core/lib/gating/api.py b/openedx/core/lib/gating/api.py
index 968ecc0246..85b5a522a7 100644
--- a/openedx/core/lib/gating/api.py
+++ b/openedx/core/lib/gating/api.py
@@ -477,7 +477,8 @@ def get_subsection_completion_percentage(subsection_usage_key, user):
             if not completable_blocks:
                 return 100
             subsection_completion_total = 0
-            course_block_completions = BlockCompletion.get_course_completions(user, subsection_usage_key.course_key)
+            course_key = subsection_usage_key.course_key
+            course_block_completions = BlockCompletion.get_learning_context_completions(user, course_key)
             for block in completable_blocks:
                 if course_block_completions.get(block):
                     subsection_completion_total += course_block_completions.get(block)
diff --git a/openedx/core/lib/gating/tests/test_api.py b/openedx/core/lib/gating/tests/test_api.py
index d51f987b06..c7fbf7de00 100644
--- a/openedx/core/lib/gating/tests/test_api.py
+++ b/openedx/core/lib/gating/tests/test_api.py
@@ -266,7 +266,7 @@ class TestGatingApi(ModuleStoreTestCase, MilestonesTestCaseMixin):
             category='html',
             display_name='some html block'
         )
-        with patch.object(BlockCompletion, 'get_course_completions') as course_block_completions_mock:
+        with patch.object(BlockCompletion, 'get_learning_context_completions') as course_block_completions_mock:
             course_block_completions_mock.return_value = {
                 problem_block.location: user_problem_completion,
                 html_block.location: user_html_completion,
@@ -307,7 +307,7 @@ class TestGatingApi(ModuleStoreTestCase, MilestonesTestCaseMixin):
             display_name=u'{} block'.format(component_type)
         )
 
-        with patch.object(BlockCompletion, 'get_course_completions') as course_block_completions_mock:
+        with patch.object(BlockCompletion, 'get_learning_context_completions') as course_block_completions_mock:
             course_block_completions_mock.return_value = {
                 component.location: completed,
             }
diff --git a/openedx/features/course_experience/tests/views/test_course_outline.py b/openedx/features/course_experience/tests/views/test_course_outline.py
index 4b86e85ea0..66017ca6c3 100644
--- a/openedx/features/course_experience/tests/views/test_course_outline.py
+++ b/openedx/features/course_experience/tests/views/test_course_outline.py
@@ -364,10 +364,12 @@ class TestCourseOutlineResumeCourse(SharedModuleStoreTestCase, CompletionWaffleT
         course_key = CourseKey.from_string(str(course.id))
         # Fake a visit to sequence2/vertical2
         block_key = UsageKey.from_string(six.text_type(sequential.location))
+        if block_key.course_key.run is None:
+            # Old mongo keys must be annotated with course run info before calling submit_completion:
+            block_key = block_key.replace(course_key=course_key)
         completion = 1.0
         BlockCompletion.objects.submit_completion(
             user=self.user,
-            course_key=course_key,
             block_key=block_key,
             completion=completion
         )
diff --git a/openedx/features/course_experience/utils.py b/openedx/features/course_experience/utils.py
index e9646bbf74..dd9bbdc01d 100644
--- a/openedx/features/course_experience/utils.py
+++ b/openedx/features/course_experience/utils.py
@@ -69,7 +69,7 @@ def get_course_outline_block_tree(request, course_id, user=None):
         if last_completed_child_position:
             # Mutex w/ NOT 'course_block_completions'
             recurse_mark_complete(
-                course_block_completions=BlockCompletion.get_course_completions(user, course_key),
+                course_block_completions=BlockCompletion.get_learning_context_completions(user, course_key),
                 latest_completion=last_completed_child_position,
                 block=block
             )
diff --git a/openedx/tests/completion_integration/test_handlers.py b/openedx/tests/completion_integration/test_handlers.py
index 344d52eb3d..f6cf616831 100644
--- a/openedx/tests/completion_integration/test_handlers.py
+++ b/openedx/tests/completion_integration/test_handlers.py
@@ -49,7 +49,7 @@ class ScorableCompletionHandlerTestCase(CompletionSetUpMixin, TestCase):
 
     def setUp(self):
         super(ScorableCompletionHandlerTestCase, self).setUp()
-        self.block_key = self.course_key.make_usage_key(block_type='problem', block_id='red')
+        self.block_key = self.context_key.make_usage_key(block_type='problem', block_id='red')
 
     def call_scorable_block_completion_handler(self, block_key, score_deleted=None):
         """
@@ -64,7 +64,7 @@ class ScorableCompletionHandlerTestCase(CompletionSetUpMixin, TestCase):
         handlers.scorable_block_completion(
             sender=self,
             user_id=self.user.id,
-            course_id=six.text_type(self.course_key),
+            course_id=six.text_type(self.context_key),
             usage_id=six.text_type(block_key),
             weighted_earned=0.0,
             weighted_possible=3.0,
@@ -83,39 +83,39 @@ class ScorableCompletionHandlerTestCase(CompletionSetUpMixin, TestCase):
         self.call_scorable_block_completion_handler(self.block_key, score_deleted)
         completion = BlockCompletion.objects.get(
             user=self.user,
-            course_key=self.course_key,
+            context_key=self.context_key,
             block_key=self.block_key,
         )
         self.assertEqual(completion.completion, expected_completion)
 
     @XBlock.register_temp_plugin(CustomScorableBlock, 'custom_scorable')
     def test_handler_skips_custom_block(self):
-        custom_block_key = self.course_key.make_usage_key(block_type='custom_scorable', block_id='green')
+        custom_block_key = self.context_key.make_usage_key(block_type='custom_scorable', block_id='green')
         self.call_scorable_block_completion_handler(custom_block_key)
         completion = BlockCompletion.objects.filter(
             user=self.user,
-            course_key=self.course_key,
+            context_key=self.context_key,
             block_key=custom_block_key,
         )
         self.assertFalse(completion.exists())
 
     @XBlock.register_temp_plugin(ExcludedScorableBlock, 'excluded_scorable')
     def test_handler_skips_excluded_block(self):
-        excluded_block_key = self.course_key.make_usage_key(block_type='excluded_scorable', block_id='blue')
+        excluded_block_key = self.context_key.make_usage_key(block_type='excluded_scorable', block_id='blue')
         self.call_scorable_block_completion_handler(excluded_block_key)
         completion = BlockCompletion.objects.filter(
             user=self.user,
-            course_key=self.course_key,
+            context_key=self.context_key,
             block_key=excluded_block_key,
         )
         self.assertFalse(completion.exists())
 
     def test_handler_skips_discussion_block(self):
-        discussion_block_key = self.course_key.make_usage_key(block_type='discussion', block_id='blue')
+        discussion_block_key = self.context_key.make_usage_key(block_type='discussion', block_id='blue')
         self.call_scorable_block_completion_handler(discussion_block_key)
         completion = BlockCompletion.objects.filter(
             user=self.user,
-            course_key=self.course_key,
+            context_key=self.context_key,
             block_key=discussion_block_key,
         )
         self.assertFalse(completion.exists())
@@ -125,7 +125,7 @@ class ScorableCompletionHandlerTestCase(CompletionSetUpMixin, TestCase):
             grades_signals.PROBLEM_WEIGHTED_SCORE_CHANGED.send_robust(
                 sender=self,
                 user_id=self.user.id,
-                course_id=six.text_type(self.course_key),
+                course_id=six.text_type(self.context_key),
                 usage_id=six.text_type(self.block_key),
                 weighted_earned=0.0,
                 weighted_possible=3.0,
@@ -145,13 +145,13 @@ class DisabledCompletionHandlerTestCase(CompletionSetUpMixin, TestCase):
 
     def setUp(self):
         super(DisabledCompletionHandlerTestCase, self).setUp()
-        self.block_key = self.course_key.make_usage_key(block_type='problem', block_id='red')
+        self.block_key = self.context_key.make_usage_key(block_type='problem', block_id='red')
 
     def test_disabled_handler_does_not_submit_completion(self):
         handlers.scorable_block_completion(
             sender=self,
             user_id=self.user.id,
-            course_id=six.text_type(self.course_key),
+            course_id=six.text_type(self.context_key),
             usage_id=six.text_type(self.block_key),
             weighted_earned=0.0,
             weighted_possible=3.0,
@@ -161,6 +161,6 @@ class DisabledCompletionHandlerTestCase(CompletionSetUpMixin, TestCase):
         with self.assertRaises(BlockCompletion.DoesNotExist):
             BlockCompletion.objects.get(
                 user=self.user,
-                course_key=self.course_key,
+                context_key=self.context_key,
                 block_key=self.block_key
             )
diff --git a/openedx/tests/completion_integration/test_models.py b/openedx/tests/completion_integration/test_models.py
index 0f6c997791..f5d725f855 100644
--- a/openedx/tests/completion_integration/test_models.py
+++ b/openedx/tests/completion_integration/test_models.py
@@ -44,7 +44,7 @@ class CompletionSetUpMixin(CompletionWaffleTestMixin):
         self.block_key = UsageKey.from_string(u'block-v1:edx+test+run+type@video+block@doggos')
         self.completion = models.BlockCompletion.objects.create(
             user=self.user,
-            course_key=self.block_key.course_key,
+            context_key=self.block_key.context_key,
             block_type=self.block_key.block_type,
             block_key=self.block_key,
             completion=0.5,
@@ -67,7 +67,6 @@ class SubmitCompletionTestCase(CompletionSetUpMixin, TestCase):
             # OTHER = user exists, completion exists
             completion, isnew = models.BlockCompletion.objects.submit_completion(
                 user=self.user,
-                course_key=self.block_key.course_key,
                 block_key=self.block_key,
                 completion=0.9,
             )
@@ -80,7 +79,6 @@ class SubmitCompletionTestCase(CompletionSetUpMixin, TestCase):
         with self.assertNumQueries(SELECT + 2 * SAVEPOINT):
             completion, isnew = models.BlockCompletion.objects.submit_completion(
                 user=self.user,
-                course_key=self.block_key.course_key,
                 block_key=self.block_key,
                 completion=0.5,
             )
@@ -94,7 +92,6 @@ class SubmitCompletionTestCase(CompletionSetUpMixin, TestCase):
         with self.assertNumQueries(SELECT + UPDATE + 4 * SAVEPOINT):
             _, isnew = models.BlockCompletion.objects.submit_completion(
                 user=newuser,
-                course_key=self.block_key.course_key,
                 block_key=self.block_key,
                 completion=0.0,
             )
@@ -106,7 +103,6 @@ class SubmitCompletionTestCase(CompletionSetUpMixin, TestCase):
         with self.assertNumQueries(SELECT + UPDATE + 4 * SAVEPOINT):
             _, isnew = models.BlockCompletion.objects.submit_completion(
                 user=self.user,
-                course_key=newblock.course_key,
                 block_key=newblock,
                 completion=1.0,
             )
@@ -117,7 +113,6 @@ class SubmitCompletionTestCase(CompletionSetUpMixin, TestCase):
         with self.assertRaises(ValidationError):
             models.BlockCompletion.objects.submit_completion(
                 user=self.user,
-                course_key=self.block_key.course_key,
                 block_key=self.block_key,
                 completion=1.2
             )
@@ -143,7 +138,6 @@ class CompletionDisabledTestCase(CompletionSetUpMixin, TestCase):
         with self.assertRaises(RuntimeError):
             models.BlockCompletion.objects.submit_completion(
                 user=self.user,
-                course_key=self.block_key.course_key,
                 block_key=self.block_key,
                 completion=0.9,
             )
@@ -167,7 +161,7 @@ class SubmitBatchCompletionTestCase(CompletionWaffleTestMixin, TestCase):
 
     def test_submit_batch_completion(self):
         blocks = [(self.block_key, 1.0)]
-        models.BlockCompletion.objects.submit_batch_completion(self.user, self.course_key_obj, blocks)
+        models.BlockCompletion.objects.submit_batch_completion(self.user, blocks)
         self.assertEqual(models.BlockCompletion.objects.count(), 1)
         self.assertEqual(models.BlockCompletion.objects.last().completion, 1.0)
 
@@ -175,19 +169,19 @@ class SubmitBatchCompletionTestCase(CompletionWaffleTestMixin, TestCase):
         with waffle.waffle().override(waffle.ENABLE_COMPLETION_TRACKING, False):
             with self.assertRaises(RuntimeError):
                 blocks = [(self.block_key, 1.0)]
-                models.BlockCompletion.objects.submit_batch_completion(self.user, self.course_key_obj, blocks)
+                models.BlockCompletion.objects.submit_batch_completion(self.user, blocks)
 
     def test_submit_batch_completion_with_same_block_new_completion_value(self):
         blocks = [(self.block_key, 0.0)]
         self.assertEqual(models.BlockCompletion.objects.count(), 0)
-        models.BlockCompletion.objects.submit_batch_completion(self.user, self.course_key_obj, blocks)
+        models.BlockCompletion.objects.submit_batch_completion(self.user, blocks)
         self.assertEqual(models.BlockCompletion.objects.count(), 1)
         model = models.BlockCompletion.objects.first()
         self.assertEqual(model.completion, 0.0)
         blocks = [
             (UsageKey.from_string('block-v1:edx+test+run+type@video+block@doggos'), 1.0),
         ]
-        models.BlockCompletion.objects.submit_batch_completion(self.user, self.course_key_obj, blocks)
+        models.BlockCompletion.objects.submit_batch_completion(self.user, blocks)
         self.assertEqual(models.BlockCompletion.objects.count(), 1)
         model = models.BlockCompletion.objects.first()
         self.assertEqual(model.completion, 1.0)
@@ -207,20 +201,25 @@ class BatchCompletionMethodTests(CompletionWaffleTestMixin, TestCase):
         self.course_key = CourseKey.from_string("edX/MOOC101/2049_T2")
         self.other_course_key = CourseKey.from_string("course-v1:ReedX+Hum110+1904")
         self.block_keys = [UsageKey.from_string("i4x://edX/MOOC101/video/{}".format(number)) for number in range(5)]
+        self.block_keys_with_runs = [key.replace(course_key=self.course_key) for key in self.block_keys]
+        self.other_course_block_keys = [self.other_course_key.make_usage_key('html', '1')]
 
-        submit_completions_for_testing(self.user, self.course_key, self.block_keys[:3])
-        submit_completions_for_testing(self.other_user, self.course_key, self.block_keys[2:])
-        submit_completions_for_testing(self.user, self.other_course_key, [self.block_keys[4]])
+        # Submit completions for the main course:
+        submit_completions_for_testing(self.user, self.block_keys_with_runs[:3])
+        # Different user:
+        submit_completions_for_testing(self.other_user, self.block_keys_with_runs[2:])
+        # Different course:
+        submit_completions_for_testing(self.user, self.other_course_block_keys)
 
-    def test_get_course_completions_missing_runs(self):
-        actual_completions = models.BlockCompletion.get_course_completions(self.user, self.course_key)
-        expected_block_keys = [key.replace(course_key=self.course_key) for key in self.block_keys[:3]]
+    def test_get_learning_context_completions_missing_runs(self):
+        actual_completions = models.BlockCompletion.get_learning_context_completions(self.user, self.course_key)
+        expected_block_keys = self.block_keys_with_runs[:3]
         expected_completions = dict(list(zip(expected_block_keys, [1.0, 0.8, 0.6])))
         self.assertEqual(expected_completions, actual_completions)
 
-    def test_get_course_completions_empty_result_set(self):
+    def test_get_learning_context_completions_empty_result_set(self):
         self.assertEqual(
-            models.BlockCompletion.get_course_completions(self.other_user, self.other_course_key),
+            models.BlockCompletion.get_learning_context_completions(self.other_user, self.other_course_key),
             {}
         )
 
diff --git a/openedx/tests/completion_integration/test_services.py b/openedx/tests/completion_integration/test_services.py
index 7bc096d629..166850ae93 100644
--- a/openedx/tests/completion_integration/test_services.py
+++ b/openedx/tests/completion_integration/test_services.py
@@ -79,7 +79,6 @@ class CompletionServiceTestCase(CompletionWaffleTestMixin, SharedModuleStoreTest
         # Proper completions for the given runtime
         BlockCompletion.objects.submit_completion(
             user=self.user,
-            course_key=self.course_key,
             block_key=self.html.location,
             completion=1.0,
         )
@@ -87,7 +86,6 @@ class CompletionServiceTestCase(CompletionWaffleTestMixin, SharedModuleStoreTest
         for idx, block_key in enumerate(self.block_keys[0:3]):
             BlockCompletion.objects.submit_completion(
                 user=self.user,
-                course_key=self.course_key,
                 block_key=block_key,
                 completion=1.0 - (0.2 * idx),
             )
@@ -96,7 +94,6 @@ class CompletionServiceTestCase(CompletionWaffleTestMixin, SharedModuleStoreTest
         for idx, block_key in enumerate(self.block_keys[2:]):
             BlockCompletion.objects.submit_completion(
                 user=self.other_user,
-                course_key=self.course_key,
                 block_key=block_key,
                 completion=0.9 - (0.2 * idx),
             )
@@ -104,8 +101,7 @@ class CompletionServiceTestCase(CompletionWaffleTestMixin, SharedModuleStoreTest
         # Wrong course
         BlockCompletion.objects.submit_completion(
             user=self.user,
-            course_key=self.other_course_key,
-            block_key=self.block_keys[4],
+            block_key=self.other_course_key.make_usage_key('problem', 'other'),
             completion=0.75,
         )
 
@@ -137,7 +133,6 @@ class CompletionServiceTestCase(CompletionWaffleTestMixin, SharedModuleStoreTest
         for block_key in self.block_keys:
             BlockCompletion.objects.submit_completion(
                 user=self.user,
-                course_key=self.course_key,
                 block_key=block_key,
                 completion=1.0
             )
@@ -153,7 +148,6 @@ class CompletionServiceTestCase(CompletionWaffleTestMixin, SharedModuleStoreTest
             # Mark all the child blocks completed except the last one
             BlockCompletion.objects.submit_completion(
                 user=self.user,
-                course_key=self.course_key,
                 block_key=self.block_keys[i],
                 completion=1.0
             )
diff --git a/openedx/tests/completion_integration/test_views.py b/openedx/tests/completion_integration/test_views.py
index 2a9c13c75c..dd9076466f 100644
--- a/openedx/tests/completion_integration/test_views.py
+++ b/openedx/tests/completion_integration/test_views.py
@@ -9,9 +9,11 @@ from completion import waffle
 from completion.test_utils import CompletionWaffleTestMixin
 from django.urls import reverse
 from rest_framework.test import APIClient
+import six
 
 from openedx.core.djangolib.testing.utils import skip_unless_lms
 from student.tests.factories import CourseEnrollmentFactory, UserFactory
+from xmodule.modulestore import ModuleStoreEnum
 from xmodule.modulestore.tests.django_utils import ModuleStoreTestCase
 from xmodule.modulestore.tests.factories import CourseFactory, ItemFactory
 
@@ -25,8 +27,11 @@ class CompletionBatchTestCase(CompletionWaffleTestMixin, ModuleStoreTestCase):
     """
     ENROLLED_USERNAME = 'test_user'
     UNENROLLED_USERNAME = 'unenrolled_user'
-    COURSE_KEY = 'TestX/101/Test'
-    BLOCK_KEY = 'i4x://TestX/101/problem/Test_Problem'
+    COURSE_KEY = 'course-v1:TestX+101+Test'
+    BLOCK_KEY = 'block-v1:TestX+101+Test+type@problem+block@Test_Problem'
+    # And for old mongo:
+    COURSE_KEY_DEPRECATED = 'TestX/201/Test'
+    BLOCK_KEY_DEPRECATED = 'i4x://TestX/201/problem/Test_Problem'
 
     def setUp(self):
         """
@@ -39,12 +44,25 @@ class CompletionBatchTestCase(CompletionWaffleTestMixin, ModuleStoreTestCase):
         self.override_waffle_switch(True)
 
         # Create course
-        self.course = CourseFactory.create(org='TestX', number='101', display_name='Test')
-        self.problem = ItemFactory.create(
-            parent=self.course,
-            category="problem",
-            display_name="Test Problem",
+        self.course = CourseFactory.create(
+            org='TestX', number='101', display_name='Test',
+            default_store=ModuleStoreEnum.Type.split,
         )
+        self.assertEqual(six.text_type(self.course.id), self.COURSE_KEY)
+        self.problem = ItemFactory.create(
+            parent=self.course, category="problem", display_name="Test Problem", publish_item=False,
+        )
+        self.assertEqual(six.text_type(self.problem.location), self.BLOCK_KEY)
+        # And an old mongo course:
+        self.course_deprecated = CourseFactory.create(
+            org='TestX', number='201', display_name='Test',
+            default_store=ModuleStoreEnum.Type.mongo,
+        )
+        self.assertEqual(six.text_type(self.course_deprecated.id), self.COURSE_KEY_DEPRECATED)
+        self.problem_deprecated = ItemFactory.create(
+            parent=self.course_deprecated, category="problem", display_name="Test Problem",
+        )
+        self.assertEqual(six.text_type(self.problem_deprecated.location), self.BLOCK_KEY_DEPRECATED)
 
         # Create users
         self.staff_user = UserFactory(is_staff=True)
@@ -53,6 +71,7 @@ class CompletionBatchTestCase(CompletionWaffleTestMixin, ModuleStoreTestCase):
 
         # Enrol one user in the course
         CourseEnrollmentFactory.create(user=self.enrolled_user, course_id=self.course.id)
+        CourseEnrollmentFactory.create(user=self.enrolled_user, course_id=self.course_deprecated.id)
 
         # Login the enrolled user by for all tests
         self.client = APIClient()
@@ -81,6 +100,16 @@ class CompletionBatchTestCase(CompletionWaffleTestMixin, ModuleStoreTestCase):
                 }
             }, 200, {'detail': 'ok'}
         ),
+        # Valid submission (old mongo)
+        (
+            {
+                'username': ENROLLED_USERNAME,
+                'course_key': COURSE_KEY_DEPRECATED,
+                'blocks': {
+                    BLOCK_KEY_DEPRECATED: 1.0,
+                }
+            }, 200, {'detail': 'ok'}
+        ),
         # Blocks list can be empty, though it's a no-op
         (
             {
@@ -97,7 +126,7 @@ class CompletionBatchTestCase(CompletionWaffleTestMixin, ModuleStoreTestCase):
                 'blocks': {
                     BLOCK_KEY: 1.0,
                 }
-            }, 400, {"detail": "Invalid course key: not:a:course:key"}
+            }, 400, {"detail": "Invalid learning context key: not:a:course:key"}
         ),
         # Block must be a valid key
         (
@@ -115,13 +144,14 @@ class CompletionBatchTestCase(CompletionWaffleTestMixin, ModuleStoreTestCase):
                 'username': ENROLLED_USERNAME,
                 'course_key': COURSE_KEY,
                 'blocks': {
-                    'i4x://some/other_course/problem/Test_Problem': 1.0,
+                    'block-v1:TestX+101+OtherCourse+type@problem+block@other': 1.0,
                 }
             },
             400,
             {
-                "detail": u"Block with key: 'i4x://some/other_course/problem/Test_Problem' is not in course {}".format(
-                    COURSE_KEY,
+                "detail": (
+                    u"Block with key: 'block-v1:TestX+101+OtherCourse+type@problem+block@other' "
+                    u"is not in context {}".format(COURSE_KEY)
                 )
             }
         ),
@@ -164,7 +194,7 @@ class CompletionBatchTestCase(CompletionWaffleTestMixin, ModuleStoreTestCase):
         (
             {
                 'username': ENROLLED_USERNAME,
-                'course_key': 'TestX/101/Test2',
+                'course_key': 'course-v1:TestX+101+Test2',
                 'blocks': {
                     BLOCK_KEY: 1.0,
                 }
@@ -191,6 +221,16 @@ class CompletionBatchTestCase(CompletionWaffleTestMixin, ModuleStoreTestCase):
                 }
             }, 200, {'detail': 'ok'}
         ),
+        # Staff can submit completion on behalf of other users (old mongo)
+        (
+            {
+                'username': ENROLLED_USERNAME,
+                'course_key': COURSE_KEY_DEPRECATED,
+                'blocks': {
+                    BLOCK_KEY_DEPRECATED: 1.0,
+                }
+            }, 200, {'detail': 'ok'}
+        ),
         # User must be enrolled in the course
         (
             {
diff --git a/requirements/edx/base.txt b/requirements/edx/base.txt
index 0ee84b72b8..8069d1f102 100644
--- a/requirements/edx/base.txt
+++ b/requirements/edx/base.txt
@@ -99,7 +99,7 @@ edx-analytics-data-api-client==0.15.3
 edx-bulk-grades==0.6.4
 edx-ccx-keys==1.0.0
 edx-celeryutils==0.3.0
-edx-completion==2.0.0
+edx-completion==3.0.1
 edx-django-oauth2-provider==1.3.5
 edx-django-release-util==0.3.1
 edx-django-sites-extensions==2.3.1
diff --git a/requirements/edx/development.txt b/requirements/edx/development.txt
index cdbd42256a..6e63f996d6 100644
--- a/requirements/edx/development.txt
+++ b/requirements/edx/development.txt
@@ -122,7 +122,7 @@ edx-analytics-data-api-client==0.15.3
 edx-bulk-grades==0.6.4
 edx-ccx-keys==1.0.0
 edx-celeryutils==0.3.0
-edx-completion==2.0.0
+edx-completion==3.0.1
 edx-django-oauth2-provider==1.3.5
 edx-django-release-util==0.3.1
 edx-django-sites-extensions==2.3.1
diff --git a/requirements/edx/testing.txt b/requirements/edx/testing.txt
index 3c2aff7cca..5e20075c96 100644
--- a/requirements/edx/testing.txt
+++ b/requirements/edx/testing.txt
@@ -118,7 +118,7 @@ edx-analytics-data-api-client==0.15.3
 edx-bulk-grades==0.6.4
 edx-ccx-keys==1.0.0
 edx-celeryutils==0.3.0
-edx-completion==2.0.0
+edx-completion==3.0.1
 edx-django-oauth2-provider==1.3.5
 edx-django-release-util==0.3.1
 edx-django-sites-extensions==2.3.1