This document provides an overview of monopolistic competition and oligopoly market structures. It defines monopolistic competition as having many differentiated product firms, easy entry and exit, and firms competing on both price and product differentiation. The document discusses how a monopolistically competitive firm sets price where marginal cost equals marginal revenue in the short run, but earns zero economic profit in the long run. It then defines oligopoly as having a small number of large firms, high barriers to entry, and the potential for both differentiated and homogeneous products. The document proceeds to describe a kinked demand curve model of non-collusive oligopoly price rigidity.