Hedonism is a family of philosophical views that prioritize pleasure. Psychological hedonism is the theory that all human behavior is motivated by the desire to maximize pleasure and minimize pain. As a form of egoism, it suggests that people only help others if they expect a personal benefit. Axiological hedonism is the view that pleasure is the sole source of intrinsic value. It asserts that other things, like knowledge and money, only have value insofar as they produce pleasure and reduce pain. This view divides into quantitative hedonism, which only considers the intensity and duration of pleasures, and qualitative hedonism, which identifies quality as another relevant factor. The closely related position of prudential hedonism states that pleasure and pain are the only factors of well-being. Ethical hedonism applies axiological hedonism to morality, arguing that people have a moral duty to pursue pleasure and avoid pain. Utilitarian versions assert that the goal is to increase overall happiness for everyone, whereas egoistic versions state that each person should only pursue their own pleasure. Outside the academic context, hedonism is sometimes used as a pejorative term for an egoistic lifestyle seeking short-term gratification.

Hedonists typically understand pleasure and pain broadly to include any positive or negative experience. While traditionally seen as bodily sensations, some contemporary philosophers view them as attitudes of attraction or aversion toward objects or contents. Hedonists often use the term "happiness" for the balance of pleasure over pain. The subjective nature of these phenomena makes it difficult to measure this balance and compare it between different people. The paradox of hedonism and the hedonic treadmill are proposed psychological barriers to the hedonist goal of long-term happiness.

As one of the oldest philosophical theories, hedonism was discussed by the Cyrenaics and Epicureans in ancient Greece, the Charvaka school in ancient India, and Yangism in ancient China. It attracted less attention in the medieval period but became a central topic in the modern era with the rise of utilitarianism. Various criticisms of hedonism emerged in the 20th century, prompting its proponents to develop new versions to address these challenges. The concept of hedonism remains relevant to many fields, ranging from psychology and economics to animal ethics.

The term hedonism refers to a family of views about the role of pleasure. These views are often categorized into psychological, axiological, and ethical hedonism depending on whether they study the relation between pleasure and motivation, value, or right action, respectively. While these distinctions are common in contemporary philosophy, earlier philosophers did not always clearly differentiate between them and sometimes combined several views in their theories. The word hedonism derives from the Ancient Greek word ἡδονή (hēdonē), meaning 'pleasure'. Its earliest known use in the English language is from the 1850s.

Psychological or motivational hedonism is the view that all human actions aim at increasing pleasure and avoiding pain. It is an empirical view about what motivates people, both on the conscious and the unconscious levels. Psychological hedonism is usually understood as a form of egoism, meaning that people strive to increase their own happiness. This implies that a person is only motivated to help others if it is in their own interest because they expect a personal benefit from it. As a theory of human motivation, psychological hedonism does not claim that all behavior leads to pleasure. For example, if a person holds mistaken beliefs or lacks necessary skills, they may attempt to produce pleasure but fail to attain the intended outcome.

The standard form of psychological hedonism asserts that the pursuit of pleasure and the avoidance of pain are the only sources of all motivation. Some psychological hedonists propose less wide-reaching formulations, suggesting that considerations of pleasure and pain are not the only source of motivation, do not influence all actions, or are otherwise limited by certain conditions. For example, reflective or rationalizing hedonism says that human motivation is only driven by pleasure and pain when people actively reflect on the overall consequences. Another version is genetic hedonism, which accepts that people desire various things besides pleasure but asserts that each desire has its origin in a desire for pleasure. Darwinian hedonism explains the pleasure-seeking tendency from an evolutionary perspective, arguing that hedonistic impulses evolved as adaptive strategies to promote survival and reproductive success.

Proponents of psychological hedonism often highlight its intuitive appeal and explanatory power. They argue that many desires focus on pleasure directly, while others aim at pleasure indirectly by promoting its causes. A similar argument from behavioral psychology proposes that altruistic conduct is learned through conditioning, which reinforces behavior that leads to positive rewards. This view asserts that all primary motivation comes from selfish drives on which all secondary motivation, including altruism, depends. Critics of psychological hedonism often cite apparent counterexamples in which people act for reasons other than their personal pleasure. Proposed examples include acts of genuine altruism, such as a soldier sacrificing themselves on the battlefield to save their comrades or a parent wanting their children to be happy. Critics also mention non-altruistic cases, like a desire for posthumous fame. It is an open question to what extent these cases can be explained as types of pleasure-seeking behavior. Another criticism from evolutionary biology argues that altruistic motivation is conducive to survival and reproduction. It suggests that altruistic motivation produces some necessary behavior, like parental care, more reliably since it does not depend on additional mechanisms, such as the individual's belief that parental care leads to personal pleasure.

Axiological or evaluative hedonism is the view that pleasure is the ultimate source of all value. It states that things other than pleasure only have value insofar as they produce pleasure or reduce pain. This is typically explained through the distinction between intrinsic and instrumental value. An entity has intrinsic value if it is good in itself or if its worth does not depend on external factors; conversely, an entity has instrumental value if it leads to other good things. According to axiological hedonism, only pleasure is intrinsically valuable because it is good even when it produces no external benefit. Money, by contrast, is only instrumentally valuable because it can be used to acquire other good things but lacks value apart from these uses. The overall value of something depends on both its intrinsic and instrumental value. In some cases, even unpleasant experiences, like a painful surgery, can be good overall if their positive consequences, like preventing future pain, outweigh the present discomfort.