Market Power
Market power is the ability of a firm, group, or actor to influence the price, quantity, quality, or terms of a market transaction — to act as a price-maker rather than a price-taker. In perfectly competitive markets, no individual actor has market power: prices are determined by aggregate supply and demand, and each participant is too small to affect them. But perfect competition is a theoretical limiting case, not an empirical norm. In most real markets, some actors possess market power, and the degree to which they possess it determines the distribution of surplus, the allocation of resources, and the rate of innovation.
Market power is not merely an economic concept. It is a systems concept: it names the condition under which a system's feedback mechanism — the price signal — is captured by a subsystem and used to serve that subsystem's interests rather than the system's overall efficiency. A monopolist restricts output to raise price not because it is irrational but because it has hacked the coordination mechanism: it has made the price signal carry information that serves its profit rather than social welfare. This is not a market failure in the sense of an externality or information asymmetry. It is a structural concentration of the market's own coordinating power.
Sources and Measures of Market Power
The canonical sources of market power are barriers to entry that prevent competitors from eroding the power-holder's advantage. These include economies of scale (lower average cost at higher output, making entry by small competitors unprofitable), network effects (the value of a good increases with the number of users, creating lock-in), control of essential resources (a critical input that cannot be duplicated), legal protection (patents, copyrights, licenses), and switching costs (the cost to consumers of moving to a competitor, which locks them in even when better alternatives exist).
The standard measure of market power is the Lerner Index: the markup of price over marginal cost as a fraction of price. A Lerner Index of zero indicates perfect competition; an index approaching one indicates monopoly. But the Lerner Index captures only static pricing power, not dynamic power — the ability to shape future market structure through investment, innovation, or predation. A firm may price at marginal cost today while building ecosystem lock-in that will give it pricing power tomorrow. The static measure misses the strategic dimension.
Market Power and Inequality
The distributive consequences of market power are severe and systematically underweighted in standard welfare economics. When a firm with market power raises prices above marginal cost, it extracts rent — income that exceeds the opportunity cost of the resources used. This rent is not a reward for productive contribution; it is a transfer from consumers to producers made possible by structural barriers rather than by superior performance. The transfer is regressive: consumption goods with market power (pharmaceuticals, telecommunications, digital platforms) are often necessities, and the rent extracted falls most heavily on those with the least ability to pay.
The connection between market power and economic inequality is direct. The firms and individuals who capture market power capture the surplus that competitive markets would distribute more broadly. The concentration of market power in technology markets — where network effects and data advantages create winner-take-all dynamics — has produced some of the largest fortunes in human history while wages for ordinary workers stagnate. This is not a coincidence. It is the predictable outcome of a system in which coordinating power is allowed to accumulate without countervailing institutional design.
The standard economic treatment of market power as a 'deviation' from competitive equilibrium gets the ontology backward. Competition is the deviation — a fragile achievement that requires active institutional maintenance. Market power is the default state of any system in which coordinating power can accumulate and concentrate. The question is not why some markets have market power; it is why any market ever lacks it. The answer — when there is one — is always political: antitrust law, regulatory design, public ownership, or countervailing institutions that prevent the natural tendency of power to compound. A economics that treats competition as natural and market power as exceptional has not understood the systems it studies.