Psychological egoism is the view that humans are always motivated by self-interest and selfishness, even in what seem to be acts of altruism. It claims that, when people choose to help others, they do so ultimately because of the personal benefits that they expect to obtain, directly or indirectly, from doing so.

This is a descriptive rather than normative view, since it only makes claims about how things are, not how they "ought to be" according to some. It is, however, related to several other normative forms of egoism, such as ethical egoism and rational egoism.

A specific form of psychological egoism is psychological hedonism, the view that the ultimate motive for all voluntary human action is the desire to experience pleasure or to avoid pain.

Immediate gratification can be sacrificed for a chance of greater, future pleasure. Further, humans are not motivated strictly to avoid pain and pursue pleasure, but rather humans will endure pain to achieve the greatest net pleasure. Accordingly, all actions are tools for increasing pleasure or decreasing pain, even those defined as altruistic and those that do not cause an immediate change in satisfaction levels.

Elliott Sober argues that psychological egoist, when pressed, often has to resort to hedonism in order to maintain their position, since the supposed pleasure of acting morally can often be the only viable explanation for an altruistic action.

The most famous psychological egoists are Pierre Bayle, and Bernard Mandeville.

Some theorists explain behavior motivated by self-interest without using pleasure and pain as the final causes of behavior.

Beginning with ancient philosophy, Epicureanism claims humans live to maximize pleasure. Epicurus argued the theory of human behavior being motivated by pleasure alone is evidenced from infancy to adulthood. Humanity performs altruistic, honorable, and virtuous acts not for the sake of another or because of a moral code but rather to increase the well-being of the self.