PIP: This paper investigates the reasons for the growth in the female labor force in the US during the 20th century. Female labor force participation rates increased by 50% from 1950 to 1970. Real wages have played a significant but hardly exclusive role both in the long term growth in female employment and in the more accelerated growth after 1950. At the beginning of this century, fewer than 1 woman in 5 was a member of the labor force; by 1981 more than 6 in 10 were. Increases in female participation were slightly larger among younger women during the 1970s; for the next 20 years the age shape tilted toward older women. For US women 25-34 years old, labor force participation rates have been rising by more than 2 percentage points per year. Closely intertwined with decisions regarding women's work are those involving marriage and family formation. 2 demographic factors that would play a part in subsequent developments are: nuclearization of the US family and urbanization. Time-series trends in education are observed because schooling affects female labor supply independently of any influence through wages; increased years of schooling across birth cohorts shows that an increase of 1.33 years of schooling increased labor participation by 6.9 percentage points during the pre-World War II era. The swing in marriage rates also affects timing, especially for younger women. Based on disaggregated time series data across the period 1950-1981, mean values at single years of age of labor supply, education, work experience, weekly wages, and fertility are determined. Profiles indicate that female labor supply varies considerably not only across cohorts but also over life cycles within birth cohorts. Results show that: 1) relative female wages defined over the work force were lower in 1980 than in 1950, 2) children, especially when young, reduce labor supply, 3) large negative elasticities are linked to female wages, and 4) with all fertility induced effects included, real wage growth explaines 58% of the postwar increase in female labor supply. Therefore, real wages do explain a considerable part of the postwar increases in female labor supply.