For more than seven centuries the <i>Mumonkan</i> has been used in Zen monasteries to train monks and to encourage the religious development of lay Buddhists. It contains forty- eight <i>koans</i>, or spiritual riddles, that must be explored during the course of Zen training. Shibayama Zenkei <i> </i>(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. <i>The Gateless Barrier </i> remains an essential text for all serious students of Buddhism.