rDzogs chen, the "Great Perfection", is a philosophical and meditational system of Tibetan Buddhism. It is the counterpart of the Ch'an in Chinese Buddhism and Zen in Japan. Western writers on Tibetan Buddhism have viewed it as a survival of the Ch'an which was once known in Tibet in the eighth century A.D., but declined after the breakup of the Tibetan empire in the mid-ninth century A.D. This view is mainly derived from the attitude of the Tibetan Buddhist orthodox schools who regarded rDzogs chen as a resurrection of Ch'an the practice of which according to the Tibetan historical tradition was officially banned after the famous Sino-Indian Buddhist controversy around 790 A.D. in Tibet. The other interesting aspect of rDzogs chen is that it is a teaching adhered to by the Buddhist school, the rNying ma pa as well as by the Bonpo (followers of the Bon religion in Tibet). Although studies in Tibetan Buddhism have advanced much in recent years, the origin and historical development of rDzogs chen has remained totally unknown. The present Study therefore focuses mainly on the origin of its theories such as "Primordial Purity" which it sees as the basis for spiritual development, and its historical and literary development. The sources for this study are mainly ninth century documents from Central Asia and texts belonging to the tenth and eleventh centuries from Tibet itself. They shed new light on the origins of rDzogs chen and its philosophical conceptions.