In The Gateless Gate, one of modern Zen Buddhism's uniquely influential masters offers classic commentaries on the Mumonkan, one of Zen's greatest collections of teaching stories. This translation was compiled with the Western reader in mind, and includes Koan Yamada's clear and penetrating comments on each case. Yamada played a seminal role in bringing Zen Buddhism to the West from Japan, going on to be the head of the Sanbo Kyodan Zen Community.

The Gateless Gate would be invaluable if only for the translation and commentary alone, yet it's loaded with extra material and is a fantastic resource to keep close by:
An in-depth Introduction to the History of Zen Practice Lineage charts Japanese-to-Chinese and Chinese-to-Japanese conversion charts for personal names, place names, and names of writings Plus front- and back-matter from ancient and modern figures: Mumon, Shuan, Kubota Ji'un, Taizan Maezumi, Hugo Enomiya-Lasalle, and Yamada Roshi's son, Masamichi Yamada.
A wonderful inspiration for the koan practitioner, and for those with a general interest in Zen Buddhism.