: This dissertation examines the effect of long work hours ("overwork") on gender inequality by examining how it affects men and women's labor market outcomes. Long work hours have become increasingly prevalent in many advanced industrial societies and established workplace norm. By working long hours, employees demonstrate professional competence and work commitment, especially in many professional and managerial jobs. By adopting a theoretical perspective emphasizing gendered organizations and institutions, I argue that although seemingly gender neutral, the overwork norm disadvantages many women, who have less time available to do paid labor because they are expected to do more housework and perform most of the caregiving responsibilities. To demonstrate this argument, I conduct three empirical analyses, which apply quantitative methods to longitudinal data drawn from the Survey of Income and Program Participation and data from the Current Population Surveys, conducted by the U.S. Census Bureau. The results show that overwork increases gender inequality in three important labor market outcomes: occupational mobility, employment, and earnings. The project has broader theoretical implications for the study of gender, social inequality, and organizations.