Within the soteriological domain of Buddhism, the Yogacara tradition can claim a special position. Applying themselves to the problem of the individual and the transformation of his psycho-physical constituents during the process of enlightenment, the masters of the Yogacara tradition developed a series of models of reality. They then manipulated these models in the terminological environment of 'fundamental transformation' (asraya-parivrtti), and its cognate forms. The vicissitudes of the forms of this manipulation parallel the development of the Yogacara as a whole, from a small meditative tradition localized in the Kashm(')ir-Gandhara area to the dominant scholastic tradition within Indian Mahayana. The dissertation is in four parts: Part I is devoted to school formation by the Yogacara. The rise of Maitreya's celestial sanction, the doxographical descriptions, model formation, the problems of synonomy, and the historical scenario of the Yogacara are all investigated in detail. Part II consists of the application of 'fundamental transformation' to the primary systems employed by the Yogacara: psycho-physical being, psychological being (alayavijnana), tripartite ontology (trisvabhava), absolute ontology (tathata), and the embryo of the Tathagata. Part III passes on to the manipulation of synthetic systems in the Yogacara. Particularly examined are the texts of the early Yogacara-- the Mahayanasutralamkara, the Abhidharmasamuccaya, the Mahayanasamgraha, and the Dharmadharmatavibhaga. Then the rise of the two scholastic centers is analyzed and their impact on 'fundamental transformation', especially in the context of the Buddhabhumisutra. Finally, in Part IV, the nature of the paths of the disciples (sravakamarga) and of the Bodhisattvas are investigated in light of their relations to the process of transformation. Particular attention is paid to the goals of the two paths, respectively understood as the 'corpus of liberation' (vimuktikaya) and the 'elemental corpus' (dharamakaya).