This document discusses different market structures including perfect competition, monopoly, monopolistic competition, and oligopoly. It provides details on the key characteristics of each market structure type and gives examples. Perfect competition has many buyers and sellers, homogeneous goods, free entry and exit, and perfect information. A monopoly has a single seller, no close substitutes for its product, and barriers to entry. Monopolistic competition features differentiated products, many firms, and independent pricing decisions. Oligopoly is characterized by a few dominant sellers, each with a significant market share.