Chapter 12 The theory of equalizing differences The chapter presents a discussion on the theory of equalizing differences. The theory of equalizing differences refers to observed wage differentials required to equalize the total monetary and nonmonetary advantages or disadvantages among work activities and among workers themselves. On the conceptual level it can make legitimate claim to be the fundamental (long run) market equilibrium construct in labor economics. Its empirical importance lies in contributing useful understanding to the determinants of the structure of wages in the economy and for making inferences about preferences and technology from observed wage data. Measurable job attributes on which compensating wage differentials have been shown to arise empirically include (1) onerous working conditions such as risks to life and health exposure to pollution and so forth; (2) intercity and interregional wage differences associated with differences in climate crime pollution and crowding; (3) special work time scheduling and related requirements including shift work inflexible work schedules and possible risks of layoff and subsequent unemployment; and (4) the composition of pay packages including vacations pensions and other fringe benefits as substitutes for direct cash wage payments. Another important class of problems identifies work environments with investment rather than with consumption. Market equilibrium is defined by equality between demand and supply for workers on each type of job.