RALPH TANNER has taught in the Universities of East Africa and London and was Chairman of the East African Institute of Social Research. He is co-author of Social Ecology of Religion and author of Transition in African Belief, the Witch Murders in Sukumaland and numerous articles on the sociology of religion. - COLIN MITCHELL served on the United Nations team assessing the Ethiopian national development plan. He has many years experience in soil survey and land evaluation, both as a project manager and a university lecturer and has worked in many areas, especially Moslem countries, southern Europe, Africa and China, including Tibet.