diff --git a/free-programming-books.md b/free-programming-books.md
index 11fe58cb2..f8095f293 100644
--- a/free-programming-books.md
+++ b/free-programming-books.md
@@ -784,6 +784,7 @@ Kerridge (PDF) (email address *requested*, not required)
 ### Agda
 
 * [Agda Tutorial](http://people.inf.elte.hu/divip/AgdaTutorial/Index.html)
+* [Programming Language Foundations in Agda](https://plfa.github.io) - Philip Wadler and Wen Kokke
 
 
 ### Alef