A discussion of the effect of market outcomes on firm behavior, consumer welfare, and market outcomes. I examine perfect competition, monopoly, oligopoly, and monopolistic competition, comparing their outcomes and when each type of structure tends to occur. Also includes a discussion of cartels, when they form, and why they tend to fail. Recommended prerequisites are Episode 48: Theory of the Firm, Episode 16: Profits and Competition, and Episode 12: The Price System.