The branch of study which investigates by scientific and historical methods the religions of the world and their mutual relations. Its successful pursuit as a science rests on the universality of religion and the frequent recurrence of certain patterns of religious experience in widely separated ethnological and social groups. It studies the conditions under which these various forms of religious behaviour manifest themselves, the processes of their growth, and the part they play in the cultures and traditions to which they belong. It is not concerned with questions of ultimate validity. It has posed problems for Christian faith by its recognition that much that was thought to be exclusive to the Christian tradition is held in common with other world religions; on the other hand it has brought out the distinctiveness of some elements in Christianity. It has also brought to Christian apologists a deeper understanding of other religions and has influenced missionary methods.