The Gateless Gate: The Classic Book of Zen Koans

Not that I read a lot of books about Zen however this is one of the best I've read. Before reading this books I've tried a couple different books about koan. They were pretty mainstream ones that did not really go deeper into the meanings and the roles of the koans. Whereas in this book, Mumon does an amazing job to explain the historical and conceptual contexts around the 40+ koans.
I really enjoyed reading them.
Whack!