The history of untouchability in India is a subject yet to be fully explored, scrutinized and reconstructed. In unraveling the elements of this complex socio-historical fabric, several questions and circumstances are salient. Foremost among them is what is the origin of the social discrimination that continues to be perpetrated upon certain social groups? What has been the relationship between social dis¬crimination and the concept of pollution or sin? These problems have special relevance to the emergence of socially discriminated groups in ancient India like the Candālas. What is the difference between social discrimination in ancient India and untouchability in medieval India? The formative process of untouchability is still clouded in this regard.. The focal point of this process might be assumed to be the post-Gupta period, but only a more minute investigation will lead to its confirmation. Then again, what is the reality of the social dis¬crimination against the depressed castes in medieval India? And finally, what were the problems inherent in the transformation of untouchability under British colonial rule and the subsequent development of the liberation movements of the depressed castes which constitute the modern phase of the problem of untouchability?