The different types of market structures are monopoly, oligopoly, perfect competition, and monopolistic competition. These structures are based on two dimensions: the number of producers in the industry and whether products are differentiated or identical. Monopoly involves a single producer selling an undifferentiated product, while oligopoly consists of a few producers selling either identical or differentiated products. Monopolistic competition features many producers selling differentiated goods, and perfect competition involves many producers offering identical products. Each type of market structure has unique characteristics that impact market behavior and outcomes.