In 1993, about 21 million persons in the United States (about one-fifth of the total in nonagricultural industries) worked part time (fewer than 35 hours a week). Although the majority of persons working part time do so voluntarily, over the past 2 decades the number of involuntary part-time workers, those who want full-time jobs but who settle for part-time work, has increased dramatically. Voluntary part timers are likely to be women aged 25-54, young people aged 16-24, or older people (aged 60 and over). Involuntary part-time workers who usually work part time are also more likely to be women aged 25-54 or young people. A much higher percentage of men are represented among the involuntary part-time workers who usually work full time, usually as the result of business cycles. All of the increase in part-time workers from 1973 to 1993 was among involuntary part-time workers who usually work part time. This increase in the ratio of part-time workers to the total is accounted for entirely by the faster growth of industries that employ many part timers. In particular, the growing share of jobs in services, retail trade, and finance, insurance, and real estate resulted in a small rise in the proportion of workers who are employed part time. As a result of the recession of 1990-91, the number and the proportion of workers who were involuntarily on part-time schedules rose but did not decrease at the end of the recession as it had in previous cycles. (KC)