 One of the most distinguishing characteristic of Kūkai’s Buddhist thought is his concept of sokushinjōbutsu, the attainment of enlightenment in this very embodied existence. This idea of sokushinjōbutsu represents the apex of Kūkai’s synthesis of Buddhist theoria and praxis. The doctrine itself is not explicit in the two major esoteric sūtras, the Dainichikyō and the Kongōchōgyō. The idea first appears rather in I-hsing’s commentary on the Dainichikyō (Ta-jih Ching Su; Commentary on the Mahāvairocana Sūtra). Kūkai was the first however to provide the idea with a systematic explication in his Sokushinjōbutsugi, which has been regarded by commentators as the most important of his philosophical expositions. Kūkai’s appropriation and systematic development of the theory takes the form of a unique philosophy of praxis that is simultaneously a philosophy of the body.