The market is made up of buyers and sellers who conduct exchange transactions. Markets can be classified based on area, the nature of transactions, volume, time period, and level of competition. Under perfect competition, there are many small firms and homogeneous products. Individual firms are price takers and maximize profits where marginal revenue equals marginal cost. Monopolies have single firms and differentiated products, allowing them to be price makers that also set output at the point where marginal revenue equals marginal cost. Oligopolies feature a few interdependent firms, and pricing may involve price leadership or tacit collusion to coordinate prices.