The document discusses different market structures and pricing under each structure. It covers the four main market structures: perfect competition, monopoly, monopolistic competition, and oligopoly. For each structure, it describes characteristics like number of firms, entry barriers, product differentiation. It then discusses pricing determination. Under perfect competition, firms are price takers and price equals marginal cost. Under monopoly, the single firm influences price by adjusting output to where marginal revenue equals marginal cost. Under monopolistic competition, in the short run firms maximize profits where marginal revenue equals marginal cost, and in the long run price equals average cost.