Using data from eleven waves of Women’s Marriage, Fertility, and Employment Survey, the authors examine trends in labor force participation among married mothers of preschool-aged children in Taiwan. The estimates indicate an upward period trend and an unexpected downward cohort trend. The results show that (1) changes in the population composition of women’s education and (2) changes in behavior for women of different levels of education, both associated with educational expansion, as well as (3) changes in economic opportunities in the labor market help explain the trends. However, changes in gendered family norms, as indicated by husband’s education, and changes in family composition factors, are largely independent of the trends. They also find that the unexpected cohort trend may be due to sample selection—women in recent birth cohorts who chose to marry and have children tend to be less committed to employment than their counterparts in earlier birth cohorts on whom the cultural constraints imposed greater pressure for them to stay home. They conclude that two major social changes—educational expansion, and industrial and economic developments—are associated with the increase in employment among married mothers of preschool-aged children in Taiwan from 1983 to 2006.