The question of nature and extent of our moral obligations to non-human animals has featured prominently in recent moral debate. This book defends the novel position that a contractarian moral theory can be used to justify the claim that animals possess a substantial and wide-ranging set of moral rights. Critiquing the rival accounts of Peter Singer and Tom Regan, this study shows how an influential form of the social contract idea can be extended to make sense of the concept of animal rights.