If we’re going to sanction criminals with loss of their liberty, then we had better have a justification for doing so. A plausible justification centers on the claim that they have committed offences that are proportionately objectionable from a moral point of view. Take that idea seriously, and the philosophy of the criminal law becomes intertwined with moral philosophy. A clear example is the topic of sexual offences. On the assumption that the moral depravity of these offences is part of the justification for punishing those who commit them, philosophers of the criminal law should be interested in the question of what makes sexual misconduct morally wrong. A popular liberal approach to answering this question focuses on consent. Roughly, the thought is that imposing sexual contact on someone without her consent is a moral wrong that should be criminalized, but the state should take no interest in sex between consenting adults. If we accept all this, then we are led to the question of what constitutes morally valid sexual consent. Clearly, this consent needs to be suitably informed, competent and free from duress. But assuming those conditions are met, what does someone actually need to do in order to consent?