diff --git a/doc/source/development_middleware.rst b/doc/source/development_middleware.rst
index e885e87e7e..6ee1d099b9 100644
--- a/doc/source/development_middleware.rst
+++ b/doc/source/development_middleware.rst
@@ -263,9 +263,9 @@ metadata items stored with an object while leaving some items unchanged.
 
 .. _sysmeta:
 
-^^^^^^^^^^^^^^^
-System Metadata
-^^^^^^^^^^^^^^^
+^^^^^^^^^^^^^^^^^^^^^^^^^
+System Metadata (Sysmeta)
+^^^^^^^^^^^^^^^^^^^^^^^^^
 
 System metadata takes the form of ``X-<type>-Sysmeta-<key>: <value>``,
 where ``<type>`` depends on the resources type (i.e. Account, Container,
@@ -303,11 +303,60 @@ individual items of user metadata is not supported. In cases where middleware
 needs to store its own metadata with a POST request, it may use Object Transient
 Sysmeta.
 
+
+^^^^^^^^^^^^^^^
+Object Metadata
+^^^^^^^^^^^^^^^
+
+Objects have other metadata in addition to the user metadata and system
+metadata described above.
+
+******************
+Immutable Metadata
+******************
+
+Objects have several items of immutable metadata. Like system metadata, these
+may only be set using PUT requests. However, they do not follow the general
+``X-Object-Sysmeta-<key>`` naming scheme and they are not automatically removed
+from client responses.
+
+Object immutable metadata includes::
+
+    X-Timestamp
+    Content-Length
+    Etag
+
+``X-Timestamp`` and ``Content-Length`` metadata MUST be included in PUT
+requests to object servers. ``Etag`` metadata is generated by object servers
+when they handle a PUT request, but checked against any ``Etag`` header sent
+with the PUT request.
+
+Object immutable metadata, along with ``Content-Type``, is the only object
+metadata that is stored by container servers and returned in object listings.
+
+************
+Content-Type
+************
+
+Object ``Content-Type`` metadata is treated differently from immutable
+metadata, system metadata and user metadata.
+
+``Content-Type`` MUST be included in PUT requests to object servers. Unlike
+immutable metadata or system metadata, ``Content-Type`` is mutable and may be
+included in POST requests to object servers. However, unlike object user
+metadata, existing ``Content-Type`` metadata persists if a POST request does
+not include new ``Content-Type`` metadata. This is because an object must have
+``Content-Type`` metadata, which is also stored by container servers and
+returned in object listings.
+
+``Content-Type`` is the only item of object metadata that is both mutable and
+yet also persists when not specified in a POST request.
+
 .. _transient_sysmeta:
 
-^^^^^^^^^^^^^^^^^^^^^^^^
+************************
 Object Transient-Sysmeta
-^^^^^^^^^^^^^^^^^^^^^^^^
+************************
 
 If middleware needs to store object metadata with a POST request it may do so
 using headers of the form ``X-Object-Transient-Sysmeta-<key>: <value>``.