This paper studies how portable skill accumulated in the labor market are. Using rich data on tasks performed in occupations, we propose the concept of task-specific human capital to measure the transferability of skills empirically. Our results on occupational mobility and wages show that labor market skills are more portable than previously considered. We find that individuals move to occupations with similar task requirements and that the distance of moves declines with time in the labor market. We also show that task-specific human capital is an important source of individual wage growth, in particular for university graduates. For them, at least 40 percent of overall wage growth over a ten year period can be attributed to task-specific human capital. For the low- and medium-skilled, task-specific human capital accounts for at least 35 and 25 percent of overall wage growth respectively.