The aim of the chapter is to develop an understanding of what moral responsibility is, so that this can, in later chapters, be applied to the case of the psychopath. I begin by distinguishing moral responsibility from other senses of responsibility, including causal, virtue, and obligation responsibility, and elucidate the various connections between these senses. I then consider the relationship between moral responsibility, praiseworthiness and blameworthiness, and the range of phenomena for which it is possible to be morally responsible. Next, I proceed to consider two major theories of moral responsibility: the Strawsonian ‘reactive attitudes’ account and the ‘reasons-responsiveness’ account. I consider the advantages and disadvantages of these, and their ability to account for a range of cases. Finally, I argue for an account adapted from R. Jay Wallace’s version of reasons-responsiveness.