This paper examines the captivity of Ottoman subjects in Russia during and after each of the empires’ eighteenth and nineteenth century conflicts. I argue that even as the Ottoman state lost these conflicts, it increasingly advanced international legal arguments to liberate these captives, with important implications for Ottoman governance and diplomacy. The paper begins with a critical moment in Ottoman-Russian relations: the 1739 Treaty of Belgrade, which ended banned the payment of ransom on both sides. Over the next half century, Ottoman subjects in Russia learned to take advantage of the rules, and they often sought help from Ottoman ambassadors sent to Russia. Yet, their freedom was not yet a major issue for the Ottoman state. This changed as the century wore on, and as the Ottomans suffered more and more devastating defeats and territorial losses. Freeing Ottoman subjects—particularly Muslims, often called “the enslaved people of Islam”—became a critical objective of Ottoman postwar diplomacy. The paper traces this shift, using the embassy reports (sefaretnames) of successive ambassadors, as well as imperial rescripts from the Ottoman archives and diplomatic correspondence from the Russian Imperial Foreign Ministry Archives. From the 1740s to the 1770s to the 1790s, Ottoman sultans became more and more insistent on freeing their subjects in Russia after each war. The story culminates in 1811-1812, as Sultan Mahmud II insisted that his defeated troops not be considered “prisoners of war,” and pressed for justice when Russian soldiers massacred hundreds of captured Ottoman civilians. These developments show an Ottoman state that, even in the midst of defeats and internal turmoil, became more and more concerned with vindicating its prestige and honor by freeing its enslaved subjects—even as it also became more confident at invoking, and defending, its rights under inter-imperial treaties. This echoed larger shifts, as the Ottoman state, especially under Mahmud, attempted to forge a stronger sense of Ottoman Muslim identity to legitimate military mobilization. In a very tangible way, “the enslaved people of Islam” embodied this identity, and their freedom was bound up with imperial prestige in a way it never had been before. The paper thus illuminates vital shifts in the relationship between the Ottoman state and its subjects, while it also reframes our understanding of the Ottomans’ engagement in international relations, and their role in the growing system of international law.