Hedonism is a philosophical system which holds that people are motivated primarily by the production of pleasure and happiness and the avoidance of pain. A person chooses his or her actions on the basis of how much pleasure and pain the actions will foreseeably cause. The word's origin is in hēdonismos, the Greek word for "delight." In the discussion of hedonism, pleasure and pain have broad meanings. Pleasure and pain refer, respectively, to all pleasurable or unpleasant feelings, experiences, states, things, properties, and events.

There are a few different types of hedonism. Motivational hedonism asserts that only pleasure and pain motivate people to do or to not do things. Normative hedonism, however, asserts that only pleasure and all types of pleasure have worth, while only pain and all types of pain have no worth. Egoistic hedonists believe that the happiness of the individual is paramount, while altruistic hedonists feel the happiness of all people is the most important.

Various philosophers, such as Plato, Aristotle, Austin, Bain, Spencer, Bentham, Moore, Sidgwick, Mill, Broad, and Ross have made contributions to the philosophy of hedonism, but the most influential were Aristippus and Epicurus. Hedonism originated with Aristippus of Cyrene, who believed that pleasure, which included physical pleasure, love, mental pleasure, moral happiness, and friendship, was the most important motivation for behavior. Aristippus also believed that long-term pleasures were more valuable than short-term pleasures. Aristippus was followed by Epicurus, who believed that mental and social pleasures were more important than physical pleasures. Epicurus also believed that pain and self-restraint had value by virtue of sometimes being necessary to health and also by providing even more pleasure through moderation.

Utilitarianism is similar to hedonism because it asserts that a person should choose his or her actions according to what is best for all people. In other words, a person should try to cause the most possible happiness for the most people possible. Most modern hedonists try to bring about pleasure, and they generally feel that the best way to do this is to make people more equal by providing more personal freedoms.