For more than seven centuries the "Mumonkan" has been used in Zen monasteries to train monks and to encourage the religious development of lay Buddhists. It contains forty- eight "koans," or spiritual riddles, that must be explored during the course of Zen training. Shibayama Zenkei " "(1894-1974), an influential Japanese Zen teacher and calligrapher who traveled and lectured throughout the United States in the 60s and 70s, offers his own commentary alongside the classic text. "The Gateless Barrier " remains an essential text for all serious students of Buddhism.