diff --git a/docs/api-reference.md b/docs/api-reference.md
index 8975655d9..890b37941 100644
--- a/docs/api-reference.md
+++ b/docs/api-reference.md
@@ -103,13 +103,16 @@ Creates a field in the given index with the given name.
 The request payload is in JSON, and may contain the `options` field. The `options` field is a JSON object which must contain a `type` along with the corresponding configuration options. 
 
 * `set`
-    * `cacheType` (string): [ranked](../data-model/#ranked) or [LRU](../data-model/#lru) caching on this field. Default is `lru`.
-    * `cacheSize` (int): Number of rows to keep in the cache. Default 50,000.
+    * `cacheType` (string): [ranked](../data-model/#ranked) or [LRU](../data-model/#lru) caching on this field. Default is `ranked`.
+    * `cacheSize` (int): Number of rows to keep in the cache. Default is 50,000.
 * `int`
     * `min` (int): Minimum integer value allowed for the field.
     * `max` (int): Maximum integer value allowed for the field.
 * `time`
     * `timeQuantum` (string): [Time Quantum](../data-model/#time-quantum) for this field.
+* `mutex`
+    * `cacheType` (string): [ranked](../data-model/#ranked) or [LRU](../data-model/#lru) caching on this field. Default is `ranked`.
+    * `cacheSize` (int): Number of rows to keep in the cache. Default is 50,000.
 
 The following example creates an `int` field called "quantity" capable of storing values from -1000 to 2000:
 
diff --git a/docs/data-model.md b/docs/data-model.md
index 4609032fc..ba7c12024 100644
--- a/docs/data-model.md
+++ b/docs/data-model.md
@@ -117,7 +117,7 @@ Query operations run in parallel, and they are evenly distributed across a clust
 
 ### Field Type
 
-Upon creation, fields are configured to be of a certain type. Pilosa supports three field types: `set`, `int`, and `time`.
+Upon creation, fields are configured to be of a certain type. Pilosa supports the following field types: `set`, `int`, `time`, and `mutex`.
 
 #### Set
 
@@ -188,3 +188,7 @@ Set(3, A=8, 2017-05-19T00:00)
 
 ![time quantum field diagram](/img/docs/field-time-quantum.svg)
 *Time quantum fueld diagram*
+
+#### Mutex
+
+Mutex fields are similar to `set` fields, with the distinction of requiring the row value for each column to be mutually exclusive. In other words, each column can only have a single value for the field. If the field value for a column is updated on a `mutex` field, then the previous field value for that column will be cleared. This field type is like a field in an RDBMS table where every record contains a single value for a particular field.
diff --git a/docs/glossary.md b/docs/glossary.md
index 550b9017b..c39a0bf6f 100644
--- a/docs/glossary.md
+++ b/docs/glossary.md
@@ -22,7 +22,7 @@ nav = []
 
 <strong id="fragment">Fragment:</strong> A Fragment is the intersection of a [field](#field) and a [shard](#shard) in an [index](#index).
 
-<strong id="field">[Field](../data-model/#field):</strong> Fields are used to group [rows](#row) into different categories. Row IDs are namespaced by field such that the same row ID in a different field refers to a different row. For [ranked](#topn) fields, rows are kept in sorted order within the field. Fields are one of three types: set, [int](#bsi), and time. For more information, see [data model](../data-model/) and [Creating fields](../api-reference/#create-field).
+<strong id="field">[Field](../data-model/#field):</strong> Fields are used to group [rows](#row) into different categories. Row IDs are namespaced by field such that the same row ID in a different field refers to a different row. For [ranked](#topn) fields, rows are kept in sorted order within the field. Fields are one of four types: set, [int](#bsi), time, and mutex. For more information, see [data model](../data-model/) and [Creating fields](../api-reference/#create-field).
 
 <strong id="frame">[Frame](../data-model/#field):</strong> Prior to Pilosa 1.0, fields were known as frames.