This document discusses monopolistic competition, which has characteristics of both monopoly and perfect competition. Under monopolistic competition, there are many firms selling differentiated products, free entry and exit into the market, and firms make profits in the short run but not the long run as new entrants drive prices down to average total cost. In the long run, monopolistically competitive firms produce at a quantity less than the efficient scale and have excess capacity. They also charge prices above marginal cost, earning a markup. Firms advertise to attract customers to their differentiated products and maintain brand names to signal quality to consumers.