This chapter introduces the readers to monopolies. After reading this chapter and working on the practice questions, the learners should be able to recognize real-world examples of monopolies, identify barriers to entry, apply the rule for profit maximization to find a monopolist’s optimal output and pricing choice, graphically show the profit or the loss of a monopolist, compare and contrast the monopoly economic outcome to the perfectly competitive one, and explain how antitrust laws are used to promote competition.