diff --git a/book/source/glossary.md b/book/source/glossary.md
index d1bad65..e84c2ec 100644
--- a/book/source/glossary.md
+++ b/book/source/glossary.md
@@ -225,6 +225,10 @@ Identity
 
 Identity Certification
     An {term}`OpenPGP Signature Packet` on an {term}`Identity Component` which {term}`certifies<Certification>` its {term}`authenticity<Authentication>`.
+    
+    Identity certifications can be issued either:
+    - by the certificate holder, as a {term}`self-signature`, or
+    - by a third party, as a {term}`third-party identity certifications<Third-party Identity Certification>`.
 
 Identity Claim
     A {term}`Certificate Holder` may use {term}`Identity Components<Identity Component>` or {term}`Notations<Notation>` to state a claim about their {term}`Identity`.