While visiting Russia in 1757, the Ottoman ambassador Shehdi Osman Pasha repeatedly came upon Ottoman subjects who claimed that, after being captured twenty years earlier, they had been kept in captivity and forced to convert to Christianity. They entreated Osman to liberate them, in accordance with the 1739 Treaty of Belgrade, but he encountered stiff resistance from Russian officials. As the century wore on, each Ottoman war was followed by similar treaty provisions, mandating the return of captives without ransom, and every ambassador encountered similar struggles over prisoners. And even as the Ottoman state struggled to redeem its subjects, the Habsburg and Romanov governments faced great difficulties in retrieving their own people who had been captured by Ottoman or Tatar forces. These struggles provide a fascinating study of the interaction between captivity, religious conversion, and diplomacy. This paper focuses on the Ottoman side of these disputes, using the sefaretnames, as well as Ottoman chronicles and archival documents, and foreign diplomatic correspondence. While such sources portray these struggles as a matter of diplomacy, as a struggle by each state to make its rival act according to its will, I argue that in fact the states struggled against their own, and their rivals' local authorities, individual owners, and captives themselves. None of the states had the absolute centralized authority that it claimed, and this presented significant challenges--the Porte could agree to return captives, but it the actual process was in the hands of kadis and governors. This was especially complicated by the interests of individual owners, who often had strong ties to local officials. My paper explores the incentive structure created by the abolition of ransom, and the Ottoman policy of paying owners a fixed price, whose value diminished through the century. Captives themselves could exercise some control over their fate by changing their religion, since every treaty specified that those who converted voluntarily would not be returned. But owners, local officials, and captives defined these provisions differently. Was conversion an act of cultural assimilation? Individual spiritual choice? Cynical manipulation of the rules? Each of these factors played a role, at least in the perception of some actors. Further, I show that states frequently came to emphasize precisely the issue which has attracted the most attention from modern scholars: individual sincerity. Thus, I provide a new perspective on one of the most significant theoretical debates on early modern religious conversion.