This paper studies how cross-country di¤erences in labor market institutions shape the pattern of international trade, focusing on workers' skill acquisition. I develop a model in which workers undertake non-contractible activities to acquire …rm-speci…c skills on the job. In the model, workers have more incentive to acquire …rm-speci…c skills relative to general skills in a more protective labor market. When sectors are di¤erent in the dependence on these two types of skills, workers'skill acquisition turns labor laws into a source of comparative advantage. By embedding the model in an open-economy framework with heterogeneous …rms, sectors with di¤erent levels of dependence on …rm-speci…c skills, and countries with varying degrees of labor protection, I show that countries with more protective labor laws export relatively more in …rm-speci…c skill-intensive sectors through both the intensive and extensive margins of trade. I then estimate returns to …rm tenure for di¤erent U.S. manufacturing sectors over the period of [1974][1975][1976][1977][1978][1979][1980][1981][1982][1983][1984][1985][1986][1987][1988][1989][1990][1991][1992][1993], and use the estimates as sector proxies for …rm-speci…c skill intensity to test the theoretical predictions. By implementing the Helpman-Melitz-Rubinstein (2008) framework to estimate sector-level gravity equations for 84 countries in 1995, I …nd supporting evidence for the predicted e¤ects of labor market institutions on both margins of trade.