An industry consists of all firms making similar or identical products. An industry’s market structure depends on the number of firms in the industry and how they compete. Here are the four basic market structures:
Perfect competition: Perfect competition happens when numerous small firms compete against each other. Firms in a competitive industry produce the socially optimal output level at the minimum possible cost per unit.
Monopoly: A monopoly is a firm that has no competitors in its industry. It reduces output to drive up prices and increase profits. By doing so, it produces less than the socially optimal output level and produces at higher costs than competitive firms.
Oligopoly: An oligopoly is an industry with only a few firms. If they collude, they reduce output and drive up profits the way a monopoly does. However, because of strong incentives to cheat on collusive agreements, oligopoly firms often end up competing against each other.
Monopolistic competition: In monopolistic competition, an industry contains many competing firms, each of which has a similar but at least slightly different product. Restaurants, for example, all serve food but of different types and in different locations. Production costs are above what could be achieved if all the firms sold identical products, but consumers benefit from the variety.