Abstract: In this article I first describe the basic principles that parents employ in disciplining their children. The description is based on a survey of parents, the major results of which are that parental sanctions are premised on wrongdoing—not on the mere causation of harm; that parental sanctions tend to be greater when wrongdoing results in harm than when it does not; that parental sanctions for intentionally harmful conduct exceed those for negligence; and that parental sanctions are not raised when the probability that wrongdoing would be discovered is low.I then develop a theory to explain the principles of discipline as functional for parents. The kernel of the theory is that the rules of discipline maximize the expected utility of parents—assuming that the utility of parents is reduced by the occurrence of harm and also reflects the well–being of their children.After elaborating the theory, I comment on several related issues, including the possible influence of childhood experience on our preferences as adults over legal rules; and I remark on the similarity between the principles of criminal law and those applied by parents in disciplining their children.