We present a theory of bureaucratic staffing in which staffers affect bureaucratic policy-making by influencing their agency’s policy priorities. The theory offers several predictions. First, presidents should appoint higher-quality staffers to agencies with policy goals that are more distant from the president. Second, presidents should be concerned with a staffer’s ideological bias only when the staffer is either sufficiently effective or when the staffer’s bias is sufficiently similar to the agency’s. Third, presidents should appoint a staffer to an agency with policy goals that are opposed to the staffer’s own, relative to the president’s goals. Fourth, less active agencies and agencies with narrow policy missions should be less likely to receive scarce staffing resources. To our knowledge, this is the first theory of political appointments to demonstrate how agencies’ structural and process-based characteristics affect the president’s incentives when making appointments.