Monopolistic competition is a type of imperfect competition such that there are many producers competing against each other but selling products that are differentiated from one another and hence not perfect substitutes. In monopolistic competition, a company takes the prices charged by its rivals as given and ignores the impact of its own prices on the prices of other companies. If this happens in the presence of a coercive government, monopolistic competition will fall into government-granted monopoly. Unlike perfect competition, the company maintains spare capacity. Models of monopolistic competition are often used to model industries. Textbook examples of industries with market structures similar to monopolistic competition include restaurants, cereals, clothing, shoes, and service industries in large cities. The "founding father" of the theory of monopolistic competition is Edward Hastings Chamberlin, who wrote a pioneering book on the subject, Theory of Monopolistic Competition (1933). Joan Robinson's book The Economics of Imperfect Competition presents a comparable theme of distinguishing perfect from imperfect competition. Further work on monopolistic competition was undertaken by Dixit and Stiglitz who created the Dixit-Stiglitz model which has proved applicable used in the sub fields of international trade theory, macroeconomics and economic geography.

In economics, imperfect competition refers to a situation where the characteristics of an economic market do not fulfil all the necessary conditions of a perfectly competitive market. Imperfect competition causes market inefficiencies, resulting in market failure. Imperfect competition usually describes behaviour of suppliers in a market, such that the level of competition between sellers is below the level of competition in perfectly competitive market conditions.