The average employed American spends more than half of their weekday, non-sleeping hours working.  Work is a critical component of most people’s lives and increasingly appreciated as a determinant of long-term health outcomes and mortality.  In this paper, I assess the extent that physical and cognitive demands of jobs held across workers' lifetimes influence their capacity for work later in life by linking Department of Labor O*Net data on job characteristics to Social Security outcomes reported by 9,818 Health and Retirement Study respondents.  I find that workers in jobs requiring manual labor are likely to transition to other manual labor jobs, though there is less persistance of advanced cognitive demands such as analytic and interpersonal skills across workers' job hisptories.  Job characteristics are also important determinants of whether individuals receive Social Security Disability Insurance (SSDI)and age benefits are first claimed.  A 1 standard deviation increase in the importance of routine manual tasks for a given job is associated with a 1.8 percentage point (12%) increase in the probability of applying for SSDI.   In contrast, a 1 standard deviation increase in non-routine, cognitive analytical tasks reduces probability of SSDI application (-2.4 percentatge points; -18%) and increases age Social Secuirty benefits are first claimed.  Policies that make it more difficult to obtain disability insurance or delay the eligibility ages for early and full Social Security retirement benefits are likely to disproportionately affect workers with current or previous tenure in physically demanding jobs.