Of the major world religions, only three, Buddhism, Christianity, and Islam have diffused widely. They were introduced across numerous socio-cultural boundaries and were received as new religions to their converts. However, these diffusing religions have had varying degrees of success from wholesale reception to wholesale rejection. This book presents the perspective that a major factor in the variations in the diffusions of these religions, and in the religions themselves, is found in the nature of the inter-group relationships between receiving groups and both sending groups and surrounding groups. A crucial perception of the receivers is the perceived contribution the new religion will make to the enhancement of important aspects of group identities and of the strength of the group. This book takes into account diffusion, an old and persistent concept in the social sciences which has been rarely applied in sociology to religions or even ideologies.