This work focuses on divine command, and in particular the theory that what makes something obligatory is that God commands it, and what makes something wrong is that God commands us not to do it. Focusing on the Abrahamic faiths, eminent scholar John E. Hare explains that two experiences have had to be integrated. The first is that God tells us to do something, or not to do something. The second is that we have to work out ourselves what to do and what not to do. The difficulty has come in establishing the proper relation between them. In Christian reflection on this, two main traditions have emerged, divine command theory and natural law theory. Hare successfully defends a version of divine command theory, but also shows that there is considerable overlap with some versions of natural law theory. He engages with a number of Christian theologians, particularly Karl Barth, and extends into a discussion of divine command within Judaism and Islam. The work concludes by examining recent work in evolutionary psychology, and argues that thinking of our moral obligations as produced by divine command offers us some help in seeing how a moral conscience could develop in a way that is evolutionarily stable.