Over the past decade, a new wave of research has restored interest in the central and complex role of bureaucracy in international politics. We introduce the concept of bureaucratic influence to unify theories modeling how bureaucrats—ranging from foreign policy advisers to international organization staff—shape behaviors ranging from international conflict to global governance. We identify two dimensions that structure the pathways through which bureaucrats exert such influence: the degree of centralization in the decision-making process and the selection criteria political leaders apply. We synthesize the resurgent literature along these dimensions, illustrating how emerging findings challenge several conventional wisdoms about the scope and nature of bureaucratic influence. Finally, we take stock of the empirical accomplishments of recent scholarship, highlighting the rich micro-level data it has introduced while noting the bureaucratic populations that remain understudied. Our review illuminates how bureaucratic actors embedded in states and international organizations shape consequential events in international politics.