utilitarianism, in normative ethics, a tradition stemming from the late 18th- and 19th-century English philosophers and economists Jeremy Bentham and John Stuart Mill according to which an action (or type of action) is right if it tends to promote happiness or pleasure and wrong if it tends to produce unhappiness or pain—not just for the performer of the action but also for everyone else affected by it.

Mill defines utilitarianism as a theory based on the principle that "actions are right in proportion as they tend to promote happiness, wrong as they tend to produce the reverse of happiness."

The doctrine that the basis of morals is utility or the greatest happiness principle, holds that actions are right in proportion as they tend to promote happiness, wrong in proportion as they tend to produce the reverse of happiness. By 'happiness' is meant pleasure and the absence of pain; by 'unhappiness' is meant pain and the lack of pleasure.

Mill was a proponent of utilitarianism, an ethical theory developed by his predecessor Jeremy Bentham. He contributed to the investigation of scientific methodology, though his knowledge of the topic was based on the writings of others, notably William Whewell, John Herschel, and Auguste Comte, and research carried out for Mill by Alexander Bain.

Mill defines “utilitarianism” as the creed that considers a particular “theory of life” as the “foundation of morals” (CW 10, 210). His view of theory of life was monistic: There is one thing, and one thing only, that is intrinsically desirable, namely pleasure.