This book is the culmination of studies carried on under Professor D. Friedman of the University of London, Yogendra Nath Tarkatirtha and Satkari Mukherji. The book is divided into four chapters. The book mainly deals with the Adhyasa theory of Sankara. Adhyasa is explained as the false suprimposition of Atman on Anatman and vice versa. The technical words 'Maya' and Avidya are used in the Vedanta philosophy to explain Adhyasa (S uperimposition) which is mithya (False). The author has tried to trace the development of these two words in the vedanta and other Indian philosophies. There is a striking similarity between the theory of the Mahayana Buddhism and the philoiophy of Sankara regarding the concept of Maya. The adhyasa theory has led to the concept of the vivarta vada. In the opinion of the author, Vivarta vada can be traced to Bhartrihari the language philosopher who existed in 691 A. 0.