diff --git a/book/source/adv/certificates.md b/book/source/adv/certificates.md
index c4ee2b6..1cf09e7 100644
--- a/book/source/adv/certificates.md
+++ b/book/source/adv/certificates.md
@@ -19,7 +19,7 @@ OpenPGP certificates are crucial for a wide range of applications, from secure e
 
 In this chapter, we aim to delve deeper into the advanced concepts surrounding OpenPGP certificates, focusing on their validity, expiration, and the critical role they play in ensuring the security and reliability of cryptographic communications. By exploring these concepts, we aim to provide readers with a comprehensive understanding of how OpenPGP certificates function within the ecosystem, their practical applications, and best practices for managing certificate validity and expiration to maintain a secure cryptographic environment.
 
-## When are certificates valid?
+## Certificate validity and expiration
 
 Certificates are composites of components that are linked together using [signatures](../signing_components).