This document provides an overview of monopolistic competition and oligopoly market structures. It discusses key characteristics of monopolistic competition, including many firms, no barriers to entry, and product differentiation. Under monopolistic competition, firms have some market power due to differentiated products and can earn profits in the short run but will break even in the long run. The document also examines models of oligopoly behavior, including collusion and Cournot models. It provides examples of industries exhibiting monopolistic competition and high concentration.