Realism in philosophy is the view that a certain kind of thing has mind-independent existence, meaning that it exists independently of anyones beliefs, linguistic practices, or conceptual schemes. It is the belief that things exist in the external world independently of our minds and perceptions. Realism can be a view about the properties of reality in general, holding that reality exists independent of the mind, as opposed to non-realist views (like some forms of skepticism and solipsism) which question the certainty of anything beyond one's own mind. Philosophers who profess realism often claim that truth consists in a correspondence between cognitive representations and reality.

Realism can be applied to various subject matters, including ethics, aesthetics, causation, modality, science, and mathematics. The dispute between realism and its opponents concerns the notion of truth appropriate for statements of the disputed class. The history of Western philosophy is checkered with disputes between those who have defended forms of realism and those who have opposed them. While there are certainly significant similarities linking the variety of positions commonly described as realist, there are also important differences which obstruct any straightforward general characterization of realism.

Realism is often contrasted with idealism, which is the belief that reality is ultimately mental or spiritual. Today, it is more usually contrasted with anti-realism, for example in the philosophy of science. Non-realism can be illustrated via error-theoretic accounts of arithmetic and morals, which show how realism about a subject-matter can be questioned on both epistemological and metaphysical grounds.