diff --git a/SUMMARY.md b/SUMMARY.md
index 7cf1d62..45b1cfd 100644
--- a/SUMMARY.md
+++ b/SUMMARY.md
@@ -23,9 +23,11 @@
   * [Status Codes](protocol/use-appropriate-status-codes.md)
   * [Caching](protocol/caching.md)
 * [Message](message/README.md)
+  * [Message Formats](message/message-formats.md)
 * [Evolution](evolution/README.md)
   * [Changes and Versioning](evolution/versioning.md)
 * [API Clients](clients/README.md)
   * [Loose Coupling](clients/loose-coupling.md)
 * [Miscellaneous](miscellaneous.md)
+* [Acknowledgements](acknowledgements.md)
 
diff --git a/acknowledgements.md b/acknowledgements.md
new file mode 100644
index 0000000..23a976c
--- /dev/null
+++ b/acknowledgements.md
@@ -0,0 +1,4 @@
+# Acknowledgements
+This work is partly based on the work of many individuals and organizations. Namely (but not exclusive to):
+
+* [Mike Amundsen](http://amundsen.com/)
diff --git a/media-types.md b/media-types.md
new file mode 100644
index 0000000..e69de29
diff --git a/message/message-formats.md b/message/message-formats.md
new file mode 100644
index 0000000..c44e9ea
--- /dev/null
+++ b/message/message-formats.md
@@ -0,0 +1,10 @@
+# Message Formats
+
+## Response Message Format
+All [`application/vnd.siren+json`](https://github.com/kevinswiber/siren)
+[`application/problem+json`](https://tools.ietf.org/html/rfc7807)
+
+
+## Request Message Format
+[`application/x-www-form-urlencoded`](https://tools.ietf.org/html/rfc1866#section-8.2.1)
+[`application/json`](http://www.json.org)