Definition of monopolistic competition

Short-run equilibrium of the firm under monopolistic competition

A monopolistically competitive firm acts like a monopolist in that the firm is able to influence the market price of its product by altering the rate of production of the product. Unlike in perfect competition, monopolistically competitive firms produce products that are not perfect substitutes. As such, brand X's product, which is different (or at least perceived to be different) from all other brands' products, is available from only a single producer. In the short-run, the monopolistically competitive firm can exploit the heterogeneity of its brand so as to reap positive economic profit (i.e. the rate of return is greater than the rate required to compensate debt and equity holders for the risk of investing in the firm). One possible effect of advertising on a firm's long run average cost curve when earning an economic profit in the short run is to raise the curve.

Long-run equilibrium of the firm under monopolistic competition

In the long-run, however, whatever distinguishing characteristic that enables one firm to reap monopoly profits will be duplicated by competing firms. This competition will drive the price of the product down and, in the long-run, the monopolistically competitive firm will make zero economic profit (i.e. a rate of return equal to the rate required to compensate debt and equity holders for the risk of investing in the firm).

Unlike in perfect competition, the monopolistically competitive firm does not produce at the lowest attainable average total cost. Instead, the firm produces at an inefficient output level, reaping more in additional revenue than it incurs in additional cost versus the efficient output level.