Shikantaza (只管打坐^?) is a Japanese term for zazen introduced by Rujing. It is associated most with the Soto school of Zen Buddhism.

The term is believed to have been first used by Dōgen's teacher Tiantong Rujing, and it literally means, "nothing but (shikan) precisely (da) sitting (za)." In other words Dōgen means by this, "doing only zazen whole-heartedly" or "single-minded sitting." Shikantaza implies "just sitting", and according to author James Ishmael Ford, "Some trace the root of this word to the pronunciation of the Pāli vipassana, though this is far from certain."

A translation of "shikantaza" offered by Kobun Chino Otogawa (1938-2002) provides some additional insight into the literal meaning of the components of the Japanese word:

Silent illumination comes from the integrated practice of shamatha (calming the mind) and vipashyana (insightful contemplation) called yuganaddha (union), and was the hallmark of the Chinese Caodong school of Ch'an. It therefore means one is practicing with both a calm mind and "questioning observation."