In moral philosophy, consequentialism is a class of normative, teleological ethical theories that holds that the consequences of one's conduct are the ultimate basis for judgement about the rightness or wrongness of that conduct. Thus, from a consequentialist standpoint, a morally right act (including omission from acting) is one that will produce a good outcome. Consequentialism, along with eudaimonism, falls under the broader category of teleological ethics, a group of views which claim that the moral value of any act consists in its tendency to produce things of intrinsic value. Consequentialists hold in general that an act is right if and only if the act (or in some views, the rule under which it falls) will produce, will probably produce, or is intended to produce, a greater balance of good over evil than any available alternative. Different consequentialist theories differ in how they define moral goods, with chief candidates including pleasure, the absence of pain, the satisfaction of one's preferences, and broader notions of the "general good".

Consequentialism is usually contrasted with deontological ethics (or deontology): deontology, in which rules and moral duty are central, derives the rightness or wrongness of one's conduct from the character of the behaviour itself, rather than the outcomes of the conduct. It is also contrasted with both virtue ethics, which is concerned with the character of the agent rather than on the nature or consequences of the act (or omission) itself, and pragmatic ethics, which treats morality like science: advancing collectively as a society over the course of many lifetimes, such that any moral criterion is subject to revision.

Some argue that consequentialist theories (such as utilitarianism) and deontological theories (such as Kantian ethics) are not necessarily mutually exclusive. For example, T. M. Scanlon advances the idea that human rights, which are commonly considered to be deontological in nature, can only be justified with reference to the consequences of having those rights. Similarly, Robert Nozick argued for a theory that is mostly consequentialist, but incorporates inviolable "side-constraints" which restrict the sort of actions agents are permitted to do. Derek Parfit argued that, in practice, when understood properly, rule consequentialism, Kantian deontology, and contractualism would all end up prescribing the same behavior.

The term consequentialism was coined by G. E. M. Anscombe in her essay "Modern Moral Philosophy" in 1958. However, the meaning of the word has changed over the time since Anscombe used it: in the sense she coined it, she had explicitly placed J. S. Mill in the nonconsequentialist and W. D. Ross in the consequentialist camp, whereas, in the contemporary sense of the word, they would be classified the other way round. This is due to changes in the meaning of the word, not due to changes in perceptions of W.D. Ross's and J.S. Mill's views.

One common view is to classify consequentialism, together with virtue ethics, under a broader label of "teleological ethics". Proponents of teleological ethics (Greek: telos, 'end, purpose' and logos, 'science') argue that the moral value of any act consists in its tendency to produce things of intrinsic value, meaning that an act is right if and only if it, or the rule under which it falls, produces, will probably produce, or is intended to produce, a greater balance of good over evil than any alternative act. This concept is exemplified by the famous aphorism, "the end justifies the means," variously attributed to Machiavelli or Ovid i.e. if a goal is morally important enough, any method of achieving it is acceptable.

Teleological ethical theories are contrasted with deontological ethical theories, which hold that acts themselves are inherently good or bad, rather than good or bad because of extrinsic factors (such as the act's consequences or the moral character of the person who acts).

Nature has placed mankind under the governance of two sovereign masters, pain and pleasure. It is for them alone to point out what we ought to do, as well as to determine what we shall do. On the one hand the standard of right and wrong, on the other the chain of causes and effects, are fastened to their throne. They govern us in all we do, in all we say, in all we think...

— Jeremy Bentham, The Principles of Morals and Legislation (1789) Ch I, p 1