Peter Byrne surveys the conceptual, ethical, social and religious issues which arise from the fact that many human beings are mentally handicapped. He explores the definition of mental handicap, its relations to IQ and the scientific study of intelligence. He examines the contention that the notion of mental handicap has no objective foundation but is merely the agent of oppression, and analyses policies and practices in paediatric medicine in relation to the mentally handicapped. Throughout, an ethical outlook committed to the moral equality of all human beings is articulated and defended. The philosophical claim that the assertion of moral equality for all human beings falls into the conceptual and ethical vice of 'speciesism' is rebutted. This important book challenges recent trends in moral philosophy and bioethics dismissing the mentally handicapped as non-persons and justifying their killing, and closes with a discussion of how far we need to buttress respect for the handicapped by a theologically grounded ethic.