diff --git a/docs/reference/clusterissuers.rst b/docs/reference/clusterissuers.rst
index 1c0c21133..049832eb1 100644
--- a/docs/reference/clusterissuers.rst
+++ b/docs/reference/clusterissuers.rst
@@ -1,3 +1,8 @@
 ==============
 ClusterIssuers
 ==============
+
+ClusterIssuers work the same as Issuers, but with an important difference:
+they issue certificates across all namespaces.
+
+The docs for Issuer resources apply equally to ClusterIssuers, with the same supported providers.