Occupational segregation by gender is one of the most salient aspects of labor markets in industrialized societies.'The vast majority of employed women in these societies work in occupations that are populated almost exclusively by women, and most men are in occupations that are disproportionately male. 2 This segregation by gender is not, of course, new. For example, Edward Gross calculates that in the United States in 1900 two-thirds of all women employed (or two-thirds of all men employed) would have had to change theirjobs for men and women to have achieved

Although David B. Tyack is not a coauthor of this article and bears no responsibility for any errors it may contain, we wish to acknowledge our intellectual debt to him. His participation during the last several years in our joint efforts to understand occupational segregation in teaching has been extremely important in developing many of the ideas in this paper. We also wish to thank Ted Mitchell and Suzanne Greenberg for painstakingly gathering data and Tyack, Mitchell, and Katherine Poss for their repeatedly voicing caveats about the data's flaws. This article was written when Lanford was at Catholic University. An earlier version of the article was presented at the annual meeting of the Social Science History Association, October 1981, Nashville, Tennessee, and benefited from comments by Alex Field and David Rogosa. The research for this article was supported by funds from the National Institute of Education (grant NIE-G-79-0020). The analyses and conclusions do not necessarily reflect the views or policies of the NIE. 1. Occupational segregation occurs when the percentage of women (or men) in an occupation deviates substantially from their percentage in the adult population or in the labor force. For purposes of this article, we define teaching as occupationally segregated when women are more than 50-55 percent of all teachers. 2. See US Department of Labor, Bureau of Labor Statistics, Perspectives on Working Women: A Data Book (Washington, DC: Government Printing Office, 1980), table 11, pp. 10-11.