The principal–agent problem (often abbreviated agency problem) refers to the conflict in interests and priorities that arises when one person or entity (the "agent") takes actions on behalf of another person or entity (the "principal"). The problem worsens when there is a greater discrepancy of interests and information between the principal and agent, as well as when the principal lacks the means to punish the agent. The deviation of the agent's actions from the principal's interest is called "agency cost".

Common examples of this relationship include corporate management (agent) and shareholders (principal), elected officials (agent) and citizens (principal), or brokers (agent) and markets (buyers and sellers, principals). In all these cases, the principal has to be concerned with whether the agent is acting in the best interest of the principal. Principal-agent models typically either examine moral hazard (hidden actions) or adverse selection (hidden information).

The principal–agent problem typically arises where the two parties have different interests and asymmetric information (the agent having more information), such that the principal cannot directly ensure that the agent is always acting in the principal's best interest, particularly when activities that are useful to the principal are costly to the agent, and where elements of what the agent does are costly for the principal to observe.

The principal and agent theory emerged in the 1970s from the combined disciplines of economics and institutional theory. There is some contention as to who originated the theory, with theorists Stephen Ross and Barry Mitnick both claiming authorship. Ross is said to have originally described the dilemma in terms of a person choosing a flavor of ice-cream for someone whose tastes they do not know (Ibid). The most cited reference to the theory, however, comes from Michael C. Jensen and William Meckling.

The theory has come to extend well beyond economics or institutional studies to all contexts of information asymmetry, uncertainty and risk.

In the context of law, principals do not know enough about whether (or to what extent) a contract has been satisfied, and they end up with agency costs. The solution to this information problem—closely related to the moral hazard problem—is to ensure the provision of appropriate incentives so agents act in the way principals wish.

In terms of game theory, it involves changing the rules of the game so that the self-interested rational choices of the agent coincide with what the principal desires. Even in the limited arena of employment contracts, the difficulty of doing this in practice is reflected in a multitude of compensation mechanisms and supervisory schemes, as well as in critique of such mechanisms as e.g., Deming (1986) expresses in his Seven Deadly Diseases of management.

In the context of the employment contract, individual contracts form a major method of restructuring incentives, by connecting as closely as optimal the information available about employee performance, and the compensation for that performance. Because of differences in the quantity and quality of information available about the performance of individual employees, the ability of employees to bear risk, and the ability of employees to manipulate evaluation methods, the structural details of individual contracts vary widely, including such mechanisms as "piece rates, [share] options, discretionary bonuses, promotions, profit sharing, efficiency wages, deferred compensation, and so on".

Typically, these mechanisms are used in the context of different types of employment: salesmen often receive some or all of their remuneration as commission, production workers are usually paid an hourly wage, while office workers are typically paid monthly or semimonthly (and if paid overtime, typically at a higher rate than the hourly rate implied by the salary). The way in which these mechanisms are used is different in the two parts of the economy which Doeringer and Piore called the "primary" and "secondary" sectors (see also dual labour market).

The secondary sector is characterised by short-term employment relationships, little or no prospect of internal promotion, and the determination of wages primarily by market forces. In terms of occupations, it consists primarily of low or unskilled jobs, whether they are blue-collar (manual-labour), white-collar (e.g., filing clerks), or service jobs (e.g., waiters). These jobs are linked by the fact that they are characterized by "low skill levels, low earnings, easy entry, job impermanence, and low returns to education or experience".

In a number of service jobs, such as food service, golf caddying, and valet parking jobs, workers in some countries are paid mostly or entirely with tips.

The use of tipping is a strategy on the part of the owners or managers to align the interests of the service workers with those of the owners or managers; the service workers have an incentive to provide good customer service (thus benefiting the company's business), because this makes it more likely that they will get a good tip.