Comparison of market structures shows how competition intensity affects firm behavior and market outcomes. Perfect Competition: Many firms, homogeneous product, P = MR = AR = MC, zero profit, fully efficient. Monopolistic Competition: Many firms, differentiated product, P > MR, price-setting power, long-run zero profit, excess capacity (inefficient). Oligopoly: Few firms, strategic interdependence, P > MR > MC, potential profit, various pricing strategies, moderate efficiency. Monopoly: One firm, unique product, MR < AR, significant pricing power, economic profit likely, allocatively inefficient. Price comparison: Perfect competition lowest, monopoly highest, oligopoly and monopolistic competition intermediate. Profit potential: Perfect competition zero, monopoly highest, others intermediate. Efficiency: Perfect competition most efficient, monopoly least efficient. Consumer welfare: Highest in perfect competition, lowest in monopoly. Innovation: Monopoly may have incentive (patent protection), perfect competition has little. ICAI tables: Often ask to fill comparison table with characteristics. Exam tip: Use reference points: "Perfect competition = most efficient, lowest price, zero profit; Monopoly = opposite."