diff --git a/README.md b/README.md
index 61e2659..588d836 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,21 @@
+<!--
+SPDX-FileCopyrightText: 2022 Paul Schaub <info@pgpainless.org>
+
+SPDX-License-Identifier: Apache-2.0
+-->
+
 # Shared PGP Certificate Directory for Java
+
+This repository contains a number of modules defining OpenPGP certificate storage for Java and Android applications.
+
+The module [pgp-certificate-store](pgp-certificate-store] defines generalized
+interfaces for OpenPGP Certificate storage.
+It can be used by applications and libraries such as
+[PGPainless](https://pgpainless.org/) for certificate management.
+
+The module [pgp-cert-d-java](pgp-cert-d-java) contains an implementation of
+the [Shared PGP Certificate Directory](https://sequoia-pgp.gitlab.io/pgp-cert-d/)
+which can also be used as a backend for the `pgp-certificate-store` interfaces.
+
+Lastly, the module [pgp-cert-d-java-jdbc-sqlite-lookup](pgp-cert-d-java-jdbc-sqlite-lookup)
+contains an implementation of the `SubkeyLookup` interface using an sqlite database.
diff --git a/pgp-certificate-store/README.md b/pgp-certificate-store/README.md
index bdbecdc..f6a0eba 100644
--- a/pgp-certificate-store/README.md
+++ b/pgp-certificate-store/README.md
@@ -6,5 +6,5 @@ SPDX-License-Identifier: Apache-2.0
 
 # PGP Certificate Store Definitions
 
-This module contains API definitions for a certificate store for PGPainless.
-A certificate store is used to store public key certificates only.
\ No newline at end of file
+This module contains API definitions for an OpenPGP certificate store.
+A certificate store is used to store public key certificates only.