The document discusses monopolistic competition and oligopoly. It defines monopolistic competition as an industry with many small firms producing differentiated products, with free entry and exit. It explores arguments for and against product differentiation and advertising. It then defines oligopoly as an industry with a small number of dominant firms, and examines models of collusion, price leadership, and game theory approaches. It concludes that oligopolies may be inefficient by pricing above costs and through wasteful strategic behavior.