This essay surveys recent scholarly work on the political theory of empire and international relations in Britain during the long nineteenth century. It traces the dominant themes and arguments to be found, points to some interpretative and methodological weaknesses, and highlights a number of topics that remain to be explored in detail. I focus on the following: the relationship between liberalism and empire and, in particular, the role played by the idea of civilization in circumscribing liberal claims to universality; the nature and evolution of international law, and the key role that jurisprudential thought played in shaping conceptions of civilization and setting the bounds of legitimacy for imperialism; the vexed relationship between the history of imperial thought and cultural/political history; and the important, though frequently marginalized, role of the colonial empire in the Victorian imperial imagination. Finally, I suggest that areas that remain to be explored in depth include non-liberal visions of international affairs; the role of theology in shaping conceptions of global order; and the balance between the United States, Europe, and the various (and very different) elements of the empire.