This is a philosophical inquiry into the moral status of animals, focusing on which ethical principle should guide us in our relationship with animals. The author examines the case for applying contractarian theory to animals other than human beings by looking in particular at the issues of rationality and trusteeship. From the law of nature and by way of a contractarian approach the author arrives at the principle of humility, which he advances as the ideal basis for our behaviour in respect of animals. He then tests certain prevailing philosophical positions in this area, including those of Singer and Regan, exploring utilitarian and rights conceptions. Finally, the author considers the significance of the principle of humility in practical terms in order to evaluate its utility as a moral judgment.