Monopolistic competition is the economic market model with many sellers selling similar, but not identical, products. The demand curve of monopolistic competition is elastic because although the firms are selling differentiated products, many are still close substitutes, so if one firm raises its price too high, many of its customers will switch to products made by other firms. This elasticity of demand makes it similar to pure competition where elasticity is perfect. Demand is not perfectly elastic because a monopolistic competitor has fewer rivals then would be the case for perfect competition, and because the products are differentiated to some degree, so they are not perfect substitutes.
Monopolistic competition has a downward sloping demand curve. Thus, just as for a pure monopoly, its marginal revenue will always be less than the market price, because it can only increase demand by lowering prices, but by doing so, it must lower the prices of all units of its product. Hence, monopolistically competitive firms maximize profits or minimize losses by producing that quantity where marginal revenue equals marginal cost, both over the short run and the long run.
