diff --git a/api/client-server/sync.yaml b/api/client-server/sync.yaml
index 3db1fa54..44351e77 100644
--- a/api/client-server/sync.yaml
+++ b/api/client-server/sync.yaml
@@ -167,11 +167,13 @@ paths:
                             this room.
                           allOf:
                           - $ref: "definitions/event_batch.yaml"
-                        "unread_notifications":
+                        unread_notifications:
                           title: Unread Notification Counts
                           type: object
                           description: |-
-                            Counts of unread notifications for this room
+                            Counts of unread notifications for this room. See the
+                            `Receiving notifications section <#receiving-notifications>`_
+                            for more information on how these are calculated.
                           properties:
                             highlight_count:
                                 title: Highlighted notification count
diff --git a/changelogs/client_server/newsfragments/2097.clarification b/changelogs/client_server/newsfragments/2097.clarification
new file mode 100644
index 00000000..68d89bcc
--- /dev/null
+++ b/changelogs/client_server/newsfragments/2097.clarification
@@ -0,0 +1 @@
+Clarify how ``unread_notifications`` is calculated.
diff --git a/specification/modules/push.rst b/specification/modules/push.rst
index 1bac0c2e..33ca7fd7 100644
--- a/specification/modules/push.rst
+++ b/specification/modules/push.rst
@@ -1,4 +1,5 @@
 .. Copyright 2016 OpenMarket Ltd
+.. Copyright 2019 The Matrix.org Foundation C.I.C.
 ..
 .. Licensed under the Apache License, Version 2.0 (the "License");
 .. you may not use this file except in compliance with the License.
@@ -116,6 +117,16 @@ have received.
 
 {{notifications_cs_http_api}}
 
+Receiving notifications
+~~~~~~~~~~~~~~~~~~~~~~~
+
+Servers MUST include the number of unread notifications in a client's ``/sync``
+stream, and MUST update it as it changes. Notifications are determined by the
+push rules which apply to an event.
+
+When the user updates their read receipt (either by using the API or by sending an
+event), notifications prior to and including that event MUST be marked as read.
+
 Push Rules
 ~~~~~~~~~~
 A push rule is a single rule that states under what *conditions* an event should
diff --git a/specification/modules/receipts.rst b/specification/modules/receipts.rst
index ee2b697a..4630091f 100644
--- a/specification/modules/receipts.rst
+++ b/specification/modules/receipts.rst
@@ -26,7 +26,8 @@ to a homeserver. To prevent this from becoming a problem, receipts are implement
 using "up to" markers. This marker indicates that the acknowledgement applies
 to all events "up to and including" the event specified. For example, marking
 an event as "read" would indicate that the user had read all events *up to* the
-referenced event.
+referenced event. See the `Receiving notifications <#receiving-notifications>`_
+section for more information on how read receipts affect notification counts.
 
 Events
 ------