This paper uses the law of war, and particularly the rules on prisoners of war, as a window on Ottoman engagement with Atlantic international law. Between the 1850s and 1880s, the Ottoman Empire increasingly engaged with the customs and scholarly traditions that had long defined rules between states in western Europe and the Atlantic world. At the same time, the Sublime Porte joined the multilateral treaties that codified the modern law of war, such as the 1856 Paris Declaration on privateering, the 1864 Geneva Convention on wounded combatants and military personnel, and the 1899 Hague Convention on the rules of war. Yet the Ottomans had a long history of signing and obeying treaties. How new, then, were these developments? I answer that question by drawing on Ottoman and British archival records to examine Ottoman policies and practices toward prisoners of war in the Crimean War (1853-1856) and Russo-Turkish War (1877-1878). This was a critical moment, as the former conflict marked the first time, in over two centuries of Ottoman-Russian rivalry, that the maritime powers of France and Britain joined the Porte. The treaty ending the Crimean War, the 1856 Treaty of Paris, welcomed the Ottomans into the “Concert of Europe”—though what this meant, in law, diplomacy, or functional politics, remains a matter of scholarly debate. The same peace conference also drew up the world’s first major multilateral agreement on the laws of war (the Paris Declaration), the paradigm for those that followed. During the latter conflict, the 1877 War, the Russian Empire used its (claimed) adherence to the newly codified law of war as evidence that it was more civilized than its Muslim imperial rivals. The Ottomans, however, fought back with their own claims of Russian legal violations. Yet through it all, I will argue, actual Ottoman captivity practices did not change much between the two conflicts, and in fact they generally, though far from universally, resembled those of their Christian allies and rivals. What changed was rhetoric, as the Ottoman state learned to play the same legal game as other major powers. The story of Ottoman engagement with the international order of the high imperialist era, then, is a matter of both continuity and change. Even as its formal legal positions changed, the Ottoman state remained flexible, pragmatic, and committed to both its own customs and to its legal obligations—which conflicted less often than one might expect.