diff --git a/29.md b/29.md
index 5b29d995..de60ad5e 100644
--- a/29.md
+++ b/29.md
@@ -200,3 +200,7 @@ It's a NIP-51-like list of pubkeys that are members of the group. Relays might c
   ]
 }
 ```
+
+## Storing the list of groups a user belongs to
+
+A definition for kind `10009` was included in [NIP-51](51.md) that allows clients to store the list of groups a user wants to remember being in.
diff --git a/51.md b/51.md
index c58d37a6..95acbc81 100644
--- a/51.md
+++ b/51.md
@@ -29,6 +29,7 @@ For example, _mute list_ can contain the public keys of spammers and bad actors
 | Public chats   | 10005 | [NIP-28](28.md) chat channels the user is in                | `"e"` (kind:40 channel definitions)                                               |
 | Blocked relays | 10006 | relays clients should never connect to                      | `"relay"` (relay URLs)                                                            |
 | Search relays  | 10007 | relays clients should use when performing search queries    | `"relay"` (relay URLs)                                                            |
+| Simple groups  | 10009 | [NIP-29](29.md) groups the user is in                       | `"group"` ([NIP-29](29.md) group ids + mandatory relay URL)                       |
 | Interests      | 10015 | topics a user may be interested in and pointers             | `"t"` (hashtags) and `"a"` (kind:30015 interest set)                              |
 | Emojis         | 10030 | user preferred emojis and pointers to emoji sets            | `"emoji"` (see [NIP-30](30.md)) and `"a"` (kind:30030 emoji set)                  |
 
diff --git a/README.md b/README.md
index fbb2897f..0ee60395 100644
--- a/README.md
+++ b/README.md
@@ -129,6 +129,7 @@ They exist to document what may be implemented by [Nostr](https://github.com/nos
 | `10005`       | Public chats list          | [51](51.md)              |
 | `10006`       | Blocked relays list        | [51](51.md)              |
 | `10007`       | Search relays list         | [51](51.md)              |
+| `10009`       | User groups                | [51](51.md), [29](29.md) |
 | `10015`       | Interests list             | [51](51.md)              |
 | `10030`       | User emoji list            | [51](51.md)              |
 | `10096`       | File storage server list   | [96](96.md)              |