The document discusses different market structures and how they influence firm behavior with respect to pricing, supply, and barriers to entry. It describes the key characteristics and examples of perfect competition, monopolistic competition, oligopoly, duopoly, and monopoly market structures. Perfect competition is defined by free entry and exit, homogeneous products, many buyers and sellers, and price-taking firms. Monopolistic competition features product differentiation and relatively free entry/exit. Oligopoly is dominated by a small number of large firms, and examples include supermarkets and oil industries. Monopoly grants a single firm control over price and supply in an industry.