diff --git a/docs/04-certificate-authority.md b/docs/04-certificate-authority.md
index 7229356..f8067e0 100644
--- a/docs/04-certificate-authority.md
+++ b/docs/04-certificate-authority.md
@@ -60,8 +60,11 @@ Results:
 ```
 ca-key.pem
 ca.pem
+ca.csr
 ```
 
+Note: `ca.csr` is a certificate signing request. It is created as an interim file and has not much use any more. It was used to generate `ca-key.pem` the private key and `ca.pem` the certificate which are two things you would use.
+
 ## Client and Server Certificates
 
 In this section you will generate client and server certificates for each Kubernetes component and a client certificate for the Kubernetes `admin` user.