In ethics, welfarism is a theory that well-being, what is good for someone or what makes a life worth living, is the only thing that has intrinsic value. In its most general sense, it can be defined as descriptive theory about what has value but some philosophers also understand welfarism as a moral theory, that what one should do is ultimately determined by considerations of well-being. The right action, policy or rule is the one leading to the maximal amount of well-being. In this sense, it is often seen as a type of consequentialism, and can take the form of utilitarianism.

It is important for various discussions and arguments about welfarism how the nature of well-being is understood. Pure welfarists hold that this value is directly determined by the individual degrees of well-being of each entity. Impure welfarists, on the other hand, include other factors related to well-being, like whether the well-being is equally distributed among sentient entities. Hedonists try to give a more substantial account of well-being by holding that all and only experiences of pleasure and pain constitute someone's well-being. This view is rejected by desire theorists, who equate well-being with desire fulfillment. Objective list theories, on the other hand, also include objective or mind-independent factors as constituents of well-being.

Diverse arguments in favor of and against welfarism are found in the academic literature. Arguments in favor often focus on general intuitions about the importance of well-being concerning most evaluative judgments. Critics of welfarism frequently concentrate on specific counterexamples in which these general intuitions seem to fail, including cases of malicious pleasures, the value of beauty and art, and the so-called "repugnant conclusion". Criticisms are sometimes addressed specifically to welfarism itself, but they also often arise within discussions of other theories, like utilitarianism or hedonism, and are directed at welfarism only implicitly by concerning the welfarist aspects of these theories. Some objections are directed specifically at pure welfarism but are avoided by impure welfarism. Welfarism has been influential in the fields of law and economics.

As a descriptive theory of value, welfarism provides a general framework for answering questions of value, such as which choices are good or which of two alternatives is better. In a more normative sense it consists of three theses: that individual well-being exists, that it has moral significance and that nothing else has moral significance.

In this sense, welfarism is the view that well-being is the only thing that has value. The value in question is usually understood as intrinsic value or what is good in itself, as contrasted with extrinsic value, which belongs to things that are useful as a means for something else.

Welfarism implies that any two outcomes that are identical in terms of well-being have the same value, no matter how much they differ otherwise. The well-being in question is usually understood in its widest sense, i.e. as the well-being not just of humans but of any sentient being. This can be articulated by stating that the value of outcomes ultimately only depends on the benefits of each one affected. Expressed in terms of possible worlds, welfarism holds that "the relative value of possible worlds is fully determined by how individuals are faring". Expressed in terms of a function, welfarism is the thesis that "the relative goodness of alternative states of affairs must be based exclusively on, and taken as an increasing function of, the respective collections of individual utilities in these states".

Welfarism as a theory of value can be interpreted as one theoretical commitment of utilitarianism together with consequentialism. Consequentialism is the theory that only acts leading to the best possible overall outcome are morally required or permissible. Consequentialism by itself leaves it open how to evaluate which of two possible outcomes is better. But this topic is addressed by welfarism. Combined, they constitute utilitarianism, i.e. the view that one should act as to produce "the greatest amount of good for the greatest number".

It is commonly accepted by many ethical theories that considerations of well-being play an important role for how one should act. Some authors see welfarism as including the ethical thesis that morality fundamentally depends on the welfare of individuals. For example, by learning that one alternative is better in terms of well-being than another, an agent usually has a reason to act such as to bring about the first rather than the second alternative. But welfarism, in its ethical sense, goes beyond this common-sense agreement by holding that, ultimately, well-being is the only thing that matters in terms of what one ought to do. This involves not just determining what is best but also includes the factor of what is in the agent's power to do, i.e. which possible actions are available to the agent. In this sense, welfarism is usually seen as a form of consequentialism, which holds that actions, policies or rules should be evaluated on the basis of their consequences.