This is a book about moral reasoning: how we actually reason and how we ought to reason. It defends a form of "rule" utilitarianism whereby we must sometimes judge and act in moral questions in accordance with generally accepted rules, so long as the existence of those rules is justified by the good they bring about. The author opposes the currently more fashionable view that it is always right for the individual to do that which produces the most good. Among the salient topics covered are: an account of the utilitarian function in society of generally accepted moral rules; a discussion of how we interpret existing moral rules and create new ones; and a defense of "rule" utilitarianism against the charge that it either commits one to irrational rule worship, or collapses into a form of "act" utilitarianism.