AbstractThis article analyzes the changing treaty law and practice governing the Ottoman state's attitude toward the subjects of its most important neighbor and most inveterate rival: the Russian Empire. The two empires were linked by both migration and unfreedom; alongside Russian slaves forcibly brought to the sultans’ domains, many others came as fugitives from serfdom and conscription. But beginning in the late 18th century, the Ottoman Empire reinforced Russian serfdom and conscription by agreeing to return fugitives, even as the same treaties undermined Ottoman forced labor by mandating the return of Russian slaves. Drawing extensively on Ottoman archival sources, this article argues that the resulting interimperial regulations on unfreedom and movement hardened the empires’ human and geographic boundaries, so that for many Russian subjects, foreign subjecthood under treaty law was not a privilege, but a liability.