This is an historical survey of the relationship between human and non-human, covering the major campaigns for reform and reviewing the shifts in attitude from the earliest times to the present day. The author's concept speciesism earns a niche in the philosophical debate that has characterized the movement over the last 15 years. The book describes this philosophical aspect and also puts forward psychological and sociological explanations. Richard Ryder describes the modernization of the RSPCA - the world's largest and oldest animal welfare organization - and the part he has played in turning animal liberation into the internationally significant media and political issue it has now become.