Fred Halliday was one of the most important scholars of his generation. This article examines Halliday's intellectual influences, assesses his contribution to International Relations (IR) and probes the broader challenges which his work raises. Halliday had a direct impact on IR through his interventions in historical sociology, revolutions and gender studies, and through his capacity to intertwine analytical, normative and political registers. More indirectly, Halliday promoted a form of critical, engaged scholarship which stands as a model for the idea of academic life as a vocation. As such, his example has much to offer current students and scholars of IR.