The document discusses different market structures: perfect competition, monopoly, monopolistic competition, and oligopoly. It provides features of each structure, examples, and criteria used to distinguish them. Perfect competition is characterized by many small sellers, homogeneous products, perfect information, and negligible impact of individual buyers/sellers on price. Monopoly has a single seller, no close substitutes for the good, and barriers to entry. Monopolistic competition involves differentiated products that are close substitutes, while oligopoly includes a small number of interdependent sellers controlling the market.