m from time to time, it is something that can happen to anyone employed. People who are simply between jobs, in this sense, are said to be frictionally unemployed. The amount of frictional unemployment depends on the frequency with which workers change jobs and the time it takes to find new ones.4 This is a particularly important category, since this category of unemployment can never be eliminated or reduced to zero. Even in the best functioning market economy, there will be some people who are between jobs. However, I think this type of unemployment could be reduced somewhat by more efficient placement services. The second form of unemployment is structural unemployment. Structural unemployment arises from an imbalance between the kinds of workers wanted by employers and the kinds of workers looking for jobs. The imbalances may be caused by inadequacy of skills, location, or personal characteristics.5 Technological developments necessitate new skills in many industries, leaving those workers who have outdated skills without a job. A plant in a declining industry may close down or move to another area, throwing out of work those employees who are unable to unwilling to move. Workers with inadequate education or training and young workers with little or no experience may be unable to get jobs because employers believe that these employees would not produce enough to be worth paying the legal minimum wage or the rate agreed upon with the union. On the other hand, even highly trained workers can be unemployed. This happened in the United States in the early 1970's, when the large numbers of new graduates with doctoral degrees in physics and mathematics exceeded the number of jobs available in those fields.6 If employers practice illegal job discrimination against any group, a high unemployment rate for those workers could result even when jobs are plentiful. Structural unemployment shows up most prominently in some cities, in some occupat...