In this class, we will derive equilibrium outcomes across a variety of market structures. We will begin by understanding equilibrium under a market structure called Perfect Competition, a benchmark construction. Economists have tools to measure the efficiency of market outcomes. We next consider the polar extreme of a competitive market: a monopoly market. We will determine the monopoly equilibrium price and quantity and efficiency properties. Much economic activity takes place in markets with just a handful of very large producers. To understand equilibrium in these oligopoly markets requires more careful attention to strategic interdependence. To capture this interdependence, we consider collusive arrangements among a small number of rivals as well as the use of simple game theoretic techniques to model equilibrium. Market Failure describes situations where markets fail to find the efficient outcome. Information asymmetries are one fertile form of market failure. Another form of market failure occurs when externalities are present. We will examine one key externality, pollution, and construct a policy prescription to mitigate the negative efficiency impacts of this externality.