The labor supply curve slopes upward: higher wages incentivize more people to enter the workforce (or work more hours).
The labor demand curve slopes downward: as wages rise, firms hire fewer workers because each additional hire becomes less profitable relative to the wage.
The downward slope of demand connects directly to diminishing marginal product of labor. As a firm adds workers while holding capital fixed, each additional worker contributes less output, so the firm's willingness to pay declines.
The intersection of these two curves determines the equilibrium wage and equilibrium employment level.

More precisely, in a competitive labor market, the firm's labor demand curve is its marginal revenue product of labor (MRPL) curve. A profit-maximizing firm hires up to the point where $MRPL = w$ , where $w$ is the wage. Since $MRPL = MPL \times P$ (marginal product times output price), the declining $MPL$ is what gives the demand curve its downward slope.

Factors Influencing Labor Curves

Several forces can shift these curves independently:

Supply shifters:

Population size and immigration (more potential workers shifts supply right)
Labor force participation rates (e.g., more women entering the workforce)
Work-leisure preferences, which can be shaped by culture, tax policy, or wealth levels

Demand shifters:

The marginal product of labor (MPL), since firms' demand for labor is a derived demand
The price of the final product (higher output prices make each worker's output more valuable, shifting $MRPL$ up)
Costs of complementary or substitute inputs (cheaper capital via automation can reduce labor demand, or cheaper raw materials can increase it)
Technological change, which can shift demand in either direction depending on whether technology complements or substitutes for labor

Elasticity matters for predicting how large the wage and employment effects of a shift will be. A steep (inelastic) supply curve means workers don't respond much to wage changes. A flat (elastic) demand curve means firms adjust hiring significantly when wages move. The Hicks-Marshall rules of derived demand give you a framework for what makes labor demand more elastic: labor demand tends to be more elastic when (1) the elasticity of substitution between labor and other inputs is higher, (2) the demand for the final product is more elastic, (3) labor's share of total costs is larger, and (4) the supply of other inputs is more elastic.

Market Dynamics and Adjustments

When supply or demand shifts, the market moves toward a new equilibrium:

If the wage is above equilibrium, there's excess supply (more workers want jobs than firms want to fill), creating unemployment.
If the wage is below equilibrium, there's excess demand (firms can't find enough workers), creating labor shortages that bid wages up.

Market forces push toward equilibrium, but adjustment isn't always instant. Wage rigidity from minimum wage laws, long-term contracts, or union agreements can prevent the market from clearing.

Factors Influencing Wage Rates

Human Capital and Productivity

Human capital theory says that investments in education, training, and skill development raise a worker's productivity, and competitive firms reward that productivity with higher wages.

Returns to education vary by field and level. A college degree in engineering typically yields a larger wage premium than a high school diploma alone, but the size of the premium depends on labor market conditions for that skill set. In the U.S., the college wage premium has roughly doubled since 1980, driven largely by rising demand for skilled labor outpacing supply growth.
General training (skills transferable across employers) tends to be paid for by the worker (through lower wages during training), since competitive firms won't fund training that other firms can poach. Firm-specific training (skills useful only at one employer) is typically shared between worker and firm: the firm pays part of the cost and the worker accepts a wage below their full productivity at that firm but above their outside option, creating a surplus that both parties share.
Technological change reshapes which skills the market values. Rising demand for data analysis and programming has increased returns to quantitative skills, while automation has reduced returns to routine manual tasks. This is the core of the skill-biased technological change hypothesis for rising wage inequality.

Labor Market Curves, The Demand for Labor | Microeconomics

Labor Market Discrimination

Even among equally productive workers, wage gaps can persist based on race, gender, age, or other characteristics. Discrimination shows up in several ways:

Wage discrimination: paying different wages for identical work
Hiring and promotion discrimination: unequal access to jobs or advancement
Occupational segregation: the concentration of certain demographic groups in lower-paying occupations or industries, which widens aggregate wage gaps
Statistical discrimination: employers use observable group characteristics (e.g., average education level of a demographic group) as a proxy when evaluating individual applicants, even when those proxies are imperfect. Unlike taste-based discrimination (where employers have a preference against a group), statistical discrimination can persist even among profit-maximizing employers because it's a rational response to imperfect information.

A key puzzle in intermediate micro: Becker's model of taste-based discrimination predicts that competitive markets should erode discrimination over time, since non-discriminating firms can hire equally productive workers at lower wages and earn higher profits. The persistence of discrimination in practice suggests either that markets aren't fully competitive, that statistical discrimination reinforces itself, or that institutional barriers sustain it.

Union Influence and Collective Bargaining

Labor unions bargain collectively on behalf of members over wages, benefits, and working conditions. This gives workers more bargaining power than they'd have negotiating individually.

The union wage premium is the difference between what union members earn and what comparable non-union workers earn for similar jobs. Empirical estimates typically put this premium at 10–20%, though it varies by industry.
Unions can raise wages above the competitive equilibrium, but this may reduce employment if firms respond by hiring fewer workers. You can think of this as the union setting a wage floor above market-clearing, creating a gap between labor supplied and labor demanded.
Union influence extends beyond their own members through threat effects: non-union firms may raise wages preemptively to discourage their workers from unionizing.

Compensating Differentials and Job Characteristics

The theory of compensating differentials explains why jobs requiring similar skill levels can pay very differently. The idea is that wages adjust to compensate for non-wage job attributes.

Jobs with undesirable features (dangerous conditions, night shifts, remote locations) tend to pay more to attract workers. For example, oil rig workers and deep-sea fishers earn premiums that reflect the physical risk involved.
Jobs with attractive non-monetary benefits (flexible hours, pleasant environment, prestige) can pay less because workers accept a lower wage in exchange.
This helps explain persistent wage differences across industries and occupations that aren't fully accounted for by human capital or discrimination. The compensating differential framework relies on workers having good information about job attributes and being mobile enough to sort across jobs; when those conditions fail, the predicted wage adjustments may not fully materialize.

Equilibrium Wage in Labor Markets

Market Clearing and Equilibrium

The equilibrium wage is the wage at which the quantity of labor supplied equals the quantity demanded. At this point, every worker willing to work at that wage finds a job, and every firm willing to pay that wage fills its positions.

In competitive labor markets, wage adjustments push toward this equilibrium. But short-run equilibrium can differ from long-run equilibrium as firms enter or exit the market, or as workers retrain and relocate.

Labor Market Curves, Demand and Supply at Work in Labor Markets | OS Microeconomics 2e

Factors Affecting Equilibrium

Supply shifts (immigration, demographic changes, shifts in participation rates) move the equilibrium wage and employment level. An increase in supply, holding demand constant, pushes wages down and employment up.
Demand shifts (technological change, industry growth or decline, changes in output prices) have the opposite pattern. An increase in demand pushes wages up and employment up.
The elasticities of supply and demand determine how much of the adjustment falls on wages versus employment. With inelastic supply, most of the effect of a demand shift shows up in wages rather than employment. With elastic supply, the effect falls more on employment.
Institutional factors like minimum wages or collective bargaining agreements can hold wages above or below the market-clearing level.

Real-World Considerations

Real labor markets deviate from the perfectly competitive model in important ways:

Monopsony is a major departure from the competitive benchmark. A monopsonistic employer (the sole or dominant buyer of labor in a market) faces an upward-sloping labor supply curve and must raise wages to attract additional workers. Because hiring one more worker raises the wage for all workers, the marginal factor cost (MFC) exceeds the wage: $MFC > w$ . The monopsonist hires where $MRPL = MFC$ , resulting in lower employment and lower wages than the competitive outcome. This model is important for understanding why minimum wages can sometimes increase employment.
Efficiency wage theory suggests some firms deliberately pay above the market-clearing wage. The logic: higher wages reduce turnover, attract better applicants, and motivate greater effort, so the productivity gains can outweigh the higher wage bill.
Search and matching frictions mean that even in equilibrium, some unemployment exists because it takes time for workers and firms to find each other. This is frictional unemployment, and it's a normal feature of any labor market.
Information asymmetry (workers don't know all available jobs; firms don't know all applicants' true productivity) slows adjustment and can lead to adverse selection in hiring.
Regional wage variation reflects differences in local cost of living, industry composition, and the tightness of local labor markets.

Government Policies on Labor Markets

Minimum Wage Legislation

A minimum wage is a price floor in the labor market. If set above the equilibrium wage, the standard competitive model predicts it will create unemployment because the quantity of labor supplied exceeds the quantity demanded at that wage.

However, the real-world impact depends on several factors:

How far above equilibrium the minimum wage is set
The elasticity of labor demand (more elastic demand means larger employment losses)
Local labor market structure (in monopsonistic markets, a minimum wage can actually increase employment by counteracting the monopsonist's incentive to restrict hiring)
Which workers are most affected (teenagers and low-skilled workers tend to be most sensitive to minimum wage changes)

The Card and Krueger (1994) study of fast-food restaurants in New Jersey and Pennsylvania found no significant employment decrease following a minimum wage increase, which challenged the simple competitive model and renewed interest in monopsony explanations. This remains one of the most debated empirical results in labor economics.

Anti-Discrimination and Equal Opportunity Policies

These laws aim to reduce wage disparities and promote equal access to employment:

Title VII of the Civil Rights Act and similar legislation prohibit discrimination in hiring, pay, and promotion.
Affirmative action policies attempt to address historical inequalities by encouraging or requiring outreach to underrepresented groups.
Pay transparency initiatives try to reduce wage discrimination by making salary information more available, reducing the information asymmetry that can allow discriminatory pay gaps to persist.
Effectiveness is debated. Enforcement is difficult, and some policies may have unintended consequences (e.g., statistical discrimination may increase if employers can't use certain screening tools).

Labor Market Regulations

Overtime pay requirements (e.g., time-and-a-half beyond 40 hours) influence how firms structure shifts and whether they hire additional workers versus extending existing workers' hours. From the firm's perspective, this creates a kink in the marginal cost of labor at 40 hours.
Occupational licensing creates barriers to entry in certain professions (doctors, electricians, barbers). This restricts labor supply in those occupations, which can raise wages for licensed workers but also raises prices for consumers.
Workplace safety regulations (like OSHA standards) increase compliance costs for employers but reduce the risk workers face, which should reduce the compensating differential for danger. The net effect on wages depends on which force dominates.

Government transfer programs interact with labor supply decisions in important ways. You can analyze most of these through the income and substitution effects framework from consumer theory:

Unemployment insurance provides income during job searches, which can improve match quality (workers find better-fitting jobs) but may also extend the duration of unemployment. The income effect of the benefit reduces the urgency to accept a job.
Social welfare benefits with income thresholds can create high effective marginal tax rates for low-wage workers, discouraging additional work. If earning an extra dollar of wages causes you to lose $0.80 in benefits, your effective marginal tax rate is 80%. This is sometimes called the poverty trap.
The Earned Income Tax Credit (EITC) is designed to avoid this problem by subsidizing wages for low-income workers, which increases the return to working and tends to boost labor force participation. The EITC has a phase-in range (where the subsidy increases with earnings, encouraging work), a plateau, and a phase-out range (where the subsidy decreases, creating a mild disincentive for additional hours).
Disability insurance programs can reduce labor force participation if the benefit level is high enough relative to available wages, creating a tradeoff between providing a safety net and maintaining work incentives.