When does a woman give valid consent to sexual relations? When does her consent render it morally or legally permissible for a man to have sexual relations with her? Why is sexual consent generally regarded as an issue about female consent? And what is the moral significance of consent? These are some of the questions discussed in this important book, which will appeal to a wide readership in philosophy, law, and the social sciences. Alan Wertheimer develops a theory of consent to sexual relations that applies to both law and morality in the light of the psychology of sexual relations, the psychology of perpetrators, and the psychology of the victims. He considers a wide variety of difficult cases such as coercion, fraud, retardation, and intoxication. We can all agree that 'no' means 'no'. This book suggests that the difficult question is whether 'yes' means 'yes'.