Koans are the single most distinctive feature of Chan, a Buddhist school in China (among other Chinese Buddhist schools, including Huayan, Tiantai, Jingtu/Pure Land, Weishi/Yogacara, and Vinaya). Chan is a phonetic translation of dhyana (meditation) in Sanskrit; it is more commonly known by its Japanese name, “Zen.” Unlike other schools of Chinese Buddhism (such as Tiantai and Hua-yan) that tend to be scholastic and theoretical, Chan made Buddhism a practical, direct, and non-scholastic way of life.

During the Tang dynasty (618–907), koanstook the form of recorded sayings; these maxims came from Zen masters and their encounters with disciples or other interlocutors. During the Song dynasty (960-1297), Linchi (Rinzai), one of the major Zen schools, developed a method that was specifically tailored for laypeople: kan hua tou. This method involved reciting, asking, and investigating a phrase or question recorded in past koans (for example, the famous “mu” koan). The method of kan hua tou is in contrast with another Zen method, mozhao (silent illumination), which was prevalent in the Caodong (Soto) School of Zen. Contemporary Rinzai in Japan still uses koans as part of its curriculum.

The most prominent collection of koans is The Blue Cliff Record (碧岩录 Bìyán Lù), which contains 100 koans compiled by Xuedou Chongxian (雪窦重显, 980-1052). It was later expanded by Yuanwu Keqin (圆悟克勤, 1063-1135). For an English translation, see
The Blue Cliff Record translated by Thomas Cleary and J.C. Cleary.

The Book of Equanimity (also known as the Book of Serenity, 从容录, Cóngróng Lù) is a collection of 100 koans by Hongzhi Zhengjue (宏智正觉, 1091–1157), compiled with commentaries by Wansong Xingxiu (1166–1246).

Perhaps the best known koan collection is The Gateless Gate (无门关，Wúménguān), with 48 koans and commentaries published in 1228 by Chinese monk Wumen (无门, 1183–1260).
For an English translation, see The Gateless Gate: The Classic Book of Zen Koans.

For a scholarly explanation of what koans are, especially on its supernatural and ritual themes, read “Introduction: What are Koans?” in Opening a Mountain—Koans of the Zen Masters by Steven Heine. For a scholarly treatment of koan tradition and its place in Chan/Zen history, read The Koan: Texts and Contexts in Zen Buddhism.

One reason why koans are so difficult to understand is that they are often expressed in a style of language where only indirect communication is intended. Koans frequently use allusions, metaphors, puns, and wordplay to deter the rational (usually binary) mind and warn people from attaching too closely to words.

Check out this video for an interesting discussion on koans.

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