Since the end of the Cold War, the relationship between international and domestic law has become one of the most pressing conundrums in legal theory and practice. But this is an old problem of politics, society and law within and between states. Despite the current urgency, no comprehensive historical study of the concepts of ‘domestic’ and ‘international’ has been produced. This thesis fills one part of this significant gap. It examines how and why these ideas, as linked terms, emerged in the works of jurists writing in the British Isles. That development is most clearly understood as a product, response and justification of projects of empire and the kinds of legal subjecthood that empire required. This history is presented in four parts. Chapter One contends that the ‘domestic’ emerged from sixteenth and seventeenth century efforts to channel natural law and imperial jurisdiction into territorial authority for the early English imperial state. Chapter Two argues that the ‘international’ appeared in the late eighteenth century to demand the rational reorganisation of the domestic laws of all states, to further commerce, check revolution, and articulate national independence. Chapter Three shows how the domestic and international became entwined in a variety of Victorian-era projects tied to the independence of absolute imperial sovereignty and the interdependence of the globalising world. Chapter Four argues that in the interwar years the domestic and international became central to juristic attempts to transform the collapsing British Empire and wider international order, culminating with general theories of the rule of law within and between states that underpinned the post-1945 settlement. This history reveals a much more diverse set of roles and projects for the domestic and international than is imagined in current theorising. The contingency of these past meanings forms one pathway for unsettling and remaking them for today’s projects.