Zen (Chinese: 禪; pinyin: Chán; Japanese: 禅, romanized: zen; Korean: 선, romanized: Seon; Vietnamese: Thiền) is a school of Mahayana Buddhism that originated in China during the Tang dynasty, known as the Chan School (Chánzong 禪宗), and later developed into various sub-schools and branches. From China, Chán spread south to Vietnam and became Vietnamese Thiền, northeast to Korea to become Seon Buddhism, and east to Japan, becoming Japanese Zen.

The term Zen is derived from the Japanese pronunciation of the Middle Chinese word 禪 (chán), an abbreviation of 禪那 (chánnà), which is a Chinese transliteration of the Sanskrit word ध्यान dhyāna ("meditation"). Zen emphasizes rigorous self-restraint, meditation-practice and the subsequent insight into nature of mind (見性, Ch. jiànxìng, Jp. kensho, "perceiving the true nature") and nature of things (without arrogance or egotism), and the personal expression of this insight in daily life, especially for the benefit of others. As such, it de-emphasizes knowledge alone of sutras and doctrine, and favors direct understanding through spiritual practice and interaction with an accomplished teacher or Master.

Zen teaching draws from numerous sources of Sarvastivada meditation practice and Mahāyāna thought, especially Yogachara, the Tathāgatagarbha sūtras, the Laṅkāvatāra Sūtra, and the Huayan school, with their emphasis on Buddha-nature, totality, and the Bodhisattva-ideal. The Prajñāpāramitā literature, as well as Madhyamaka thought, have also been influential in the shaping of the apophatic and sometimes iconoclastic nature of Zen rhetoric.

Furthermore, the Chan School was also influenced by Taoist philosophy, especially Neo-Daoist thought.