This is a revised and updated edition of the book that gave rise to the Animal Liberation Movement. When first published, in 1975, it put forward a radically new conception of the relationship that ought to exist between human beings and non-human animals. It argues against speciesism, that is the exploitation of one species by another, as well as the moral necessity of vegetarianism and explains how outdated our views towards animals are. This book also features factual material on animal experimentation and factory farming as well as recent developments in the Animal Liberation Movement.