Tiantai is a school of Chinese Buddhism named for Mount Tiantai in Zhejiang province, where its effective founder, the monk Zhiyi (538-597), taught in the sixth century. It was among the first distinctively Chinese, as opposed to imported Indian, schools of Buddhism, and it is celebrated for the systematic comprehensiveness with which Zhiyi organised the whole inherited mass of Buddhist scripture and doctrine into a single coherent scheme.
Tiantai takes the Lotus Sutra as the highest and most complete of the Buddha's teachings, and on its basis Zhiyi devised a famous system of doctrinal classification (panjiao) that ranked the various sutras as successive stages in the Buddha's pedagogy, culminating in the Lotus. At the heart of Tiantai philosophy stands the Threefold Truth (that all phenomena are simultaneously empty of intrinsic nature, provisionally existent, and both at once in a middle that includes them), and the teaching of the mutual inclusion of all realms of existence in a single moment of thought (the "three thousand realms in one thought-moment"). With this went an elaborate programme of calming-and-insight meditation.