The document discusses different market structures including perfect competition, monopoly, monopolistic competition, oligopoly, and duopoly. It describes the key characteristics of each structure such as the number of firms, level of control over price, barriers to entry/exit, product homogeneity, and interdependence between firms. Perfect competition has many small firms, identical products, free entry/exit and firms are price takers. A monopoly is dominated by a single firm. Oligopoly and duopoly are dominated by a small number of large firms where their actions influence each other.