Nearly all workers have a supervisor or ‘boss’. Yet little is known about how bosses influence the quality of employees’ lives. This study is a cautious attempt to provide new formal evidence. First, it is shown that a boss’s technical competence is the single strongest predictor of a worker’s job satisfaction. Second, it is demonstrated in longitudinal data -- after controlling for fixed effects -- that even if a worker stays in the same job and workplace a rise in the competence of a supervisor is associated with an improvement in the worker’s well-being. Third, a variety of robustness checks, including tentative instrumental-variable results, are reported. These findings, which draw on US and British data, contribute to an emerging literature on the role of expert leaders in organizations. Finally, the paper discusses potential weaknesses of existing evidence and necessary future research.