Why have so many young men withdrawn from the U.S. labor force since 1965? This paper presents a model in which men invest time in employment to enhance their value as marriage partners. When the marriage market return on this investment declines, young men’s employment declines as well, in preparation for a less favorable marriage market. Taking this prediction to data, I show that fewer young men sought employment after 2 interventions that reduced the value of gender-role-specialization within marriage: i) the adoption of unilateral divorce legislation, and ii) demand-driven improvements in women’s employment opportunities. I then show, using a structural estimation, that half of the employment effect of a labor market shock to men’s wages is determined by endogenous adjustment of the marriage market to the shock. These findings establish the changing marriage market as an important driver of decline in young men’s labor market involvement.