Utilitarianism is the ethical theory that the production of happiness and reduction of unhappiness should be the standard by which actions are judged right or wrong and by which the rules of morality, laws, public policies, and social institutions are to be critically evaluated. According to utilitarianism, an action is not right or wrong simply because it is a case of telling the truth or lying; and the moral rule against lying is not in itself correct. Lying is wrong because, in general, it has bad consequences. And the moral rule against lying can be subjected to empirical study to justify some cases of lying, such as to avoid a disastrous consequence in saving someone's life.

Utilitarianism is one of the major ethical philosophies of the last two hundred years, especially in the English-speaking world. Even if there are few philosophers who call themselves utilitarians, those who are not utilitarians often regard utilitarianism as the most important alternative philosophy, the one to be replaced by their own. Examples of the latter are intuitionists, such as E. F. Carritt and W. D. Ross, early in the twentieth century, and, more recently, John Rawls, whose book A Theory of Justice contrasts his principles of justice with utilitarian principles and contrasts his contractarian foundation for his principles with the grounds for utilitarian principles. Some of the most prominent ethical philosophers of recent years have explicitly considered themselves utilitarians. Examples would be Richard Brandt, J. J. C. Smart, and R. M. Hare.