Mahāyāna Mahāparinirvāṇa Sūtra
The Tiantai school takes the "Lotus Sūtra" ("") as the main basis, the "Mahāprajñāpāramitāupadeśa" of Nāgārjuna as the guide, the "Mahāyāna Mahāparinirvāṇa Sūtra" as the support, and the "Pañcaviṃśatisāhasrikā Prajñāpāramitā Sūtra" (The Prajñāpāramitā Sūtra in 25,000 Lines) for methods of contemplation. The “Book of the Original Acts that Adorn the Bodhisattva,” ("Pusa yingluo benye jing" T. 24, No. 1485) is also a key text. Tiantai is often termed the ‘Four Sutras One Treatise School’ (四経一論) because of the strong influence of these texts on the tradition.