This document summarizes different market structures: - Perfect competition has many small firms, identical products, price set by buyers, and no barriers to entry. Examples include agriculture. - Monopolistic competition has many firms selling differentiated but similar products with some control over price and low barriers to entry, like jeans and sunglasses. - Oligopoly has a market dominated by a few large firms that are interdependent with significant barriers to entry, like airlines and breakfast cereal. Firms may use predatory pricing, collusion, or conglomeration to control their industries legally. - Monopoly has a single seller with barriers to entry that allow high prices without competition, like public utilities. The document provides