diff --git a/book/source/04-certificates.md b/book/source/04-certificates.md
index 028a37b..d55bfb0 100644
--- a/book/source/04-certificates.md
+++ b/book/source/04-certificates.md
@@ -376,6 +376,10 @@ Some implementations, such as Sequoia, prefer to rely on the full historical set
 
 An example for the tension between minimization and nuanced verification of the [temporal validity](temporal-validity) of signatures can be seen in the case of [rpm-sequoia](https://github.com/rpm-software-management/rpm-sequoia/issues/50#issuecomment-1689642607). To handle the limited availability of historical self-signatures on certificates in the wild, the rpm-sequoia implementation was adjusted to accept self-signatures that predate the existing self-signature for the signing key.
 
+#### Autocrypt
+
+The Autocrypt Level 1 specification defines a specific [minimal format for OpenPGP certificates](https://autocrypt.org/level1.html#openpgp-based-key-data) that are distributed by the autocrypt mechanism.
+
 #### Autocrypt/WKD minimization
 
 Email clients depend only on a limited subset of the components of certificates. Thus, it's possible to use a smaller view of that certificate, which is easier to transfer by mail user-agents.