Purity-Pollution is an universal phenomenon found in all the known societies in the world. Purity of mind, body and soul is believed to be essentially required to approach the divine objects. Pollution occuring due to birth, death, menstruation, puberty etc. is commonly observed by the people including tribals, Muslims and Christians in India. But, purity-pollution as a principle of caste system is unique in Indian social reality. Untouchability is the outcome of this principle where persons belonging to the so called untouchable castes or scheduled castes are hateful to the persons belonging to the higher castes. This book is an attempt to understand different issues and problems relating to the caste system in India, such as purity-pollution, nature and sources of purity-pollution, hierarchical gradation of various castes and sub-castes, separation of castes/jatis and discrimination of one caste from another, division of labour or jajmani system and to deprive some persons of their rights as human beings, practice of untouchability and the like.