This dissertation investigates the historical construction of the foreigner as a category of subjectivity. It does so by tracing a set of procedures and regulations devised by British imperial authorities to bring the Gulf pearl industry, which was one of the largest sources of natural pearls in the world for several millennia, under their control in the period between the signing of the first Anglo-Arab treaty at the turn of the nineteenth century and the effective demise of Gulf pearling in the early 1930s. I argue that imperial concerns about the mobility of pearl fishers shaped the production of this novel category of subject, the migrant foreigner, in three ways. In the first place, the yearly influx of scores of pearl fishers to the shaikhdoms that lined the Gulf's western littoral at the advent of the main diving season hindered British attempts to establish expansive jurisdictional claims in these polities. It was in the context of the effort to rein in the excesses of pearling labor mobility that British imperial institutions were first constructed in the Gulf shaikhdoms. In the second place, Britain also shaped the comportment of these mariners by policing their movement. Since Britain portrayed itself as a guardian of the Gulf pearl trade through the treaties and agreements it signed with Gulf shaikhs throughout the nineteenth century, it restricted behaviors that it considered detrimental to the success of that trade. Chief among these was the ability of indebted pearl fishers to run away to neighboring shaikhdoms to take on a fresh cash advance unencumbered by the debt they had accumulated elsewhere, a practice that British officials deemed absconding. In the third place, Britain eventually institutionalized the measures it took to govern migrant pearl fishers in the shaikhdom of Bahrain, which became ground zero for British operations in the region from 1900 onward. In doing so, British officials incorporated methods of governance initially devised to regulate the movement of an itinerant group of workers within the juridical scope of their jurisdiction over all foreigners in Bahrain. By demonstrating the constitutive effects of this effort, which rendered deportations and constraints on collective labor agitation a regular tool in the repertoire of imperial and shaikhly power, this dissertation presents a new way to understand the nature and legacies of British rule in the Gulf and a different set of historical coordinates to locate the origins of the foreign worker as a category of legal and political subjectivity in the region.