Much scholarly ink has been spilled on the question of border-making in the interwar Middle East, particularly with regard to the mandate system’s carving up of the old Ottoman Arab provinces into separate (though not independent) nation-states and its production of particular forms of colonial citizenship in the process. Considerably less attention has been paid to the ways in which this largely military enforcement of borders also deliberately and knowingly produced citizenship’s opposite, statelessness. This paper investigates how mandatory governments in Palestine, Iraq, Syria, and Lebanon understood the production and meaning of statelessness for refugees, migrants, and longstanding inhabitants alike in these newly designated national spaces. By the time Britain and France occupied their new mandatory possessions in the aftermath of the First World War, it was already clear that refugees would be an important aspect of defining new forms of nation-statehood at the levels of local territoriality, the formation of national citizen bodies, and a new international legal regime that defined, enforced, and defended differentiated levels of political sovereignty. In particular, colonial and internationalist authorities made distinct use of Armenian and Assyrian statelessness to delineate particular visions of nation-statehood in the mandatory territories of Syria, Lebanon, and Iraq. But non-refugee communities emerged as stateless as well; certain Bedouin tribes, for instance, who were assigned a political status that allowed them to move across new national borders (for instance, between Palestine and Syria) but that restricted their claims to political representation. Above all, by limiting the rights of movement, representation, and political process for Arabs in interwar Palestine, these same mandatory authorities were gradually and deliberately defining Palestinian Arabs in toto as a comparable stateless community, paving the way for the international acceptance of the eventual transformation of Palestinians into stateless refugees. Statelessness represented a useful tool in the arsenal of colonial state-building strategies: it helped to delineate both physical borders and the limits of citizenship, created pools of populations whose rights were permanently up for colonial negotiation and coercion, and provided maneuvering room for the bolstering of some claims to nationhood over others. The production of statelessness was, then, a central aspect of the colonial production of territoriality as the League and the mandatory powers sought to shape a post-Ottoman Middle East to serve their own political, strategic, and material requirements.