This thesis examines the Śrīvaiṣṇava tradition's validation of the doctrine of surrendering oneself to a Personal God (prapatti). Prapatti was mentioned by Rāmānuja, the tradition's most authoritative teacher, as an auxiliary to bhaktiyoga that he taught as a means to mokṣa. After the time of Rāmānuja, prapatti was developed as an alternative means. In order to validate the doctrine of prapatti, the post-Rāmānuja teachers were committed to arguing that Rāmānuja taught prapatti as an independent means to mokṣa (aṅgi-prapatti). I focus on Vedāntadeśika, the most famous post-Rāmānuja teacher, and his interpretation of Rāmānuja's prapatti. I argue that, in his Nikṣeparakṣā, Vedāntadeśika reinterpreted Rāmānuja's teaching of prapatti as a teaching of aṅgi-prapatti. Vedāntadeśika's interpretation reflects his harmonization of Rāmānuja's incoherent statements regarding prapatti and synthesization of both intra- and extra-traditional authorities. This study ultimately shows Vedāntadeśika's intellectual contribution and the role of his interpretation in the doctrinal validation of aṅgi-prapatti.