Criticism is an evaluative or corrective exercise that can occur in any area of human life. Criticism can therefore take many different forms. How people go about criticizing, can vary a great deal. In specific areas of human endeavour, the form of criticism can be highly specialized and technical; it often requires professional knowledge to appreciate the criticism. For subject-specific information, see the Varieties of criticism page.

To criticize does not necessarily imply "to find fault", but the word is often taken to mean the simple expression of an object against prejudice, no matter positive or negative. Often criticism involves active disagreement, but it may only mean "taking sides". Constructive criticism will often involve an exploration of the different sides of an issue. Criticism is often presented as something unpleasant, but there are friendly criticisms, amicably discussed, and some people find great pleasure in criticism ("keeping people sharp", "providing the critical edge").

Literary criticism (or literary studies) is the study, evaluation, and interpretation of literature. Modern literary criticism is often influenced by literary theory, which is the philosophical discussion of literature's goals and methods. Though the two activities are closely related, literary critics are not always, and have not always been, theorists.

Whether or not literary criticism should be considered a separate field of inquiry from literary theory, or conversely from book reviewing, is a matter of some controversy. For example, the Johns Hopkins Guide to Literary Theory and Criticism draws no distinction between literary theory and literary criticism, and almost always uses the terms together to describe the same concept. Some critics consider literary criticism a practical application of literary theory, because criticism always deals directly with particular literary works, while theory may be more general or abstract.