Gateless Gate (Chinese, Wu-men kuan; Jap., Mumonkan). A collection of kōans compiled by the Chinese Ch'an master Wu-men Hui-k'ai (1183-1260) and published in 1229. It contains 48 stories of Ch'an encounters between various well-known Chinese Ch'an figures that shows a decisive moment in their teaching. These stories, given in a very condensed form, are accompanied by Wu-men's own comments and a short poem. It gained wide currency in China, Japan, Korea, and more recently, in Europe and America.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)