The four main market structures are perfect competition, monopolistic competition, monopoly, and oligopoly.

First of all, perfect competition is comprised of many firms producing homogeneous goods or services with no firm having any sort of market power. This results in them being price-takers and not price-setters. Profit is maximized when equating marginal revenue with marginal cost. Price is also equal to marginal revenue.

Secondly, monopolistic competition is comprised of many firms producing slightly differentiated goods or services. This results in firms operating with some level of market power in the short run but act as perfectly competitive firms in the long run. Profit is maximized by equating marginal revenue with marginal cost to get equilibrium output but equilibrium price set at the point where quantity intersects with the demand curve.

Thirdly, a monopoly consists of a market with just one firm having total control of the market share. This makes the firm a price-setter. Profit is maximized by artificially inflating prices through limiting supply. This is done by equating marginal revenue with marginal cost to derive equilibrium quantity and following that by plugging in the equilibrium quantity into the demand curve to solve for equilibrium price.

Lastly, an oligopoly consists of a market with just a few firms dominating market share. Other than that it is very similar to a monopoly setting in which high barriers to entry exist as well as the few firms being price-setters. The profit maximization process of oligopolies is similar to monopolies. One oligopoly model however represents a kinked demand curve to illustrate how if one firm cuts prices the others in the market will follow suit to gain back market share, but if one firm increases prices the other firms will not emulate.