Tiantai, also known as T'ien-t'ai, is an East Asian school of Mahāyāna Buddhism that originated in China during the 6th century. It is recognized as one of the most influential Buddhist traditions within both China and Japan. The school is noted by scholars for being the earliest attempt at a thoroughgoing Sinitic reworking of Indian Buddhist traditions.
The tradition draws from earlier Mahāyāna sources, specifically Madhyamaka, with Nāgārjuna traditionally regarded as its first patriarch. Tiantai Buddhism emphasizes the "One Vehicle" doctrine derived from the Lotus Sūtra and incorporates the philosophy of Zhiyi, who served as the school's fourth patriarch and principal founder.