This paper focuses on key administrative aspects of the Ottoman/Polish-Lithuanian frontier in the 16th and 17th centuries. In a frontier where the southern borderlands were governed mainly through the Ottoman vassal polities, the Porte continued to find ways to exert direct control through the ordering of space and forging relationships with emerging local powers. Employing a range of Ottoman, Polish, Ukrainian, Russian and Romanian sources, this study explicates two strategies employed by the Sublime Porte in response to new challenges to Ottoman rule in the northern frontier: first, the creation of directly administered eyalets of Özü/Silistre (1621) and Kameniçe (1672), an act that was accompanied by the repeated mutual demarcation of borders with Poland-Lithuania, and second, the co-opting of clients from both sides of the frontier. These projects repeatedly led to ambiguous episodes of co-dominium. By examining the results of these processes, I engage established studies of Ottoman frontier zones and contribute to our understanding of Ottoman administrative practice and sovereignty in the periphery. In the early 17th century, external conflicts and the rise of the Budjak Horde and Zaporozhian Cossacks upset the balance between Ottoman Sultans, Polish-Lithuanian Kings, Crimean Khans and the Voyevodes of Moldavia. The acute upheavals that ensued on both sides of the frontier included “rogue” Ottoman beylerbeyis such as Abaza Mehmed Pasha carrying out private wars, the emergence of the Cossack Hetmanate (which briefly submitted to Ottoman rule) and several attempts by Tatar leaders to submit to Polish-Lithuanian monarchs. Both Ottoman and Polish-Lithuanian sovereigns were therefore forced to incorporate these emerging power brokers in their efforts to establish direct and indirect rule in a rapidly changing frontier. Studies employing sources from both sides of this 1,200 kilometer-long frontier have begun to emerge in Ottoman historiography. There remain, however, lingering questions regarding the administrative practices of republic and sultanate vis-à-vis competing notions of sovereignty rooted in multiple traditions of patronage and jurisprudence. By engaging sources from both sides of the Ottoman/Polish-Lithuanian frontier, it is possible to better understand how Ottoman vassals and directly appointed administrators maintained relationships of economy, political alliance and consanguinity with the sovereign powers and local frontier notables of neighboring Poland-Lithuania. In critical cases, these relations predated and continued to develop parallel to legal states of clientage to the Padishah. By establishing patterns of inter-imperial connectivity, we can better understand what appear to be top-down administrative projects in this under-studied frontier context.