This paper develops and structurally estimates a labor market model that integrates job assignment, learning, and human capital acquisition to account for the main patterns of careers in firms. A key innovation is that the model incorporates workers’ job mobility within and between firms, and the possibility that, through job assignment, firms affect the rate at which they acquire information about workers. The model is estimated using longitudinal administrative data on managers from one U.S. firm in a service industry (the data of Baker, Gibbs, and Holmström (1994a,b)) and fits the data remarkably well. The estimated model is used to assess both the direct effect of learning on wages and its indirect effect through its impact on the dynamics of job assignment. Consistent with the evidence in the literature on comparative advantage and learning, the estimated direct effect of learning on wages is found to be small. Unlike in previous work, by jointly estimating the dynamics of beliefs, jobs, and wages imposing all of the model restrictions, the impact of learning on job assignment can be uncovered and the indirect effect of learning on wages explicitly assessed. The key finding of the paper is that the indirect effect of learning on wages is substantial: overall learning accounts for one quarter of the cumulative wage growth on the job during the first seven years of tenure. Nearly all of the remaining growth is from human capital acquisition. A related novel finding is that the experimentation component of learning is a primary determinant of the timing of promotions and wage increases. Along with persistent uncertainty about ability, experimentation is responsible for substantially compressing wage growth at low tenures.