In Industrial Organization we study the relation between industry structure and market outcomes. Basic microeconomics teaches us that competitive markets—characterized, among other things, by the presence of many firms—yield economic efficient outcomes. Industrial Organization, on the other hand, focuses on the potential departures from efficiency in markets with fewer than many participants. Firms’ behavior and interaction, and, therefore, the achieved level of efficiency in such markets depend on a number of parameters and the aim of this course is to investigate some of these possibilities. Topics covered include non-uniform pricing by a monopoly, quantity and price competition, cartels and collusion, product differentiation, firm entry and exit, and matching markets.