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Tiantai (Chinese and Japanese: 天台宗; pinyin: tiāntāi zōng; ) is an important school of Buddhism in China, Japan, Korea, and Vietnam. In Japan the school is known as Tendai-shū, and in Korea it is known as Cheontae.

The name is derived from the fact that Chih-i, the fourth patriarch, lived on Mount Tiantai. Tiantai is sometimes also called "The Lotus School", after the central role of the Lotus Sutra in its teachings.

During the Tang Dynasty, the Tiantai school became one of the leading schools of Chinese Buddhism, with numerous large temples supported by emperors and wealthy patrons, with many thousands of monks and millions of followers.

Most scholars regard the Tiantai as one of the first truly Chinese schools of Buddhist thought. The schools of Buddhism that had existed in China prior to the emergence of the Tiantai are generally believed to represent direct transplantations from India, with little modification to their basic doctrines and methods. The creation of the Tiantai school signified the maturation and integration of Buddhism in the Chinese context. No longer content to simply translate texts received from Indian sources, Chinese Buddhists began to apply new analyses to old texts, and even to produce new scriptures and commentaries that would attain significant status within the East Asian sphere.