Taking as its subject the Russo-Ottoman borderland during the period between the Treaty of Berlin (1878) and the start of the First World War (1914), and making extensive use of Ottoman archival documents covering this period, this thesis focuses on the ways in which the Ottoman state attempted to establish two types of boundary in order to ensure sovereignty over its territory. Firstly, there was a new geo-political border, the line dividing the Russian and Ottoman Empires at the juncture of north-eastern Anatolia and the southern Caucasus, created by the Treaty of Berlin. Secondly, there was what can be called a citizenship boundary, shaped by various laws and regulations defining the Ottoman citizenry. The main issues examined in respect of the first boundary are various types of human movement across this border and their control by the Ottoman state. Primary concerns regarding the second boundary revolve around the inclusion in and exclusion from the Ottoman citizenship of ethno-religious groups as a result of the Ottoman state's enforcement of the border. Our approach to studying how the citizenship boundary was established is two-fold, reflecting both local and state perspectives. The local perspective shows the actions of the inhabitants and travellers passing through this border region as shaped by their own day-to-day needs, livelihood patterns and pre-existing socio-economic relations; these resisted limitation by the logic of the sovereign state. The state perspective reflects the Ottoman view of Russia as the main threat to its border territories; this view led the Ottoman central authorities to perceive the entanglements and overlapping positions of its subjects in and with Russia as the cause of their ambiguous loyalties to the Ottoman state. In focusing on the specific policies and practices that the Ottoman state applied in order to deal with this ambiguity, two groups of people, Muslims and Armenians, are singled out. Notwithstanding the all-embracing state laws and discourse of legal equality, Ottoman border policy in respect of its Muslim subjects is shown to have differed greatly from that designed for its Armenian subjects. Therefore, the thesis offers a nuanced framework with which to understand Ottoman citizenship in the Russo-Ottoman border context, by revealing the normative and practical measures the Ottoman state employed to classify its Muslim and Armenian populations, thereby differentiating their status as subjects. This thesis - the first English-language work on the Russo-Ottoman border region during the late nineteenth century and pre-WWI period- offers a range of original insights into this borderland in particular and related issues more generally. It unfolds the details of everyday life and represents the local people as active agents - active, moreover, in relation both to the changing nature and effectiveness of the state's assertion of territorial authority and also to the differences between the two empires' policies and practices. Overall, the thesis focuses on the end-of-empire border politics and the issue of Ottoman citizenship not only from the perspective of macro-level political developments and central state power but also in terms of the peripheral specificities of administration and the movements and subjecthood choices of villagers. Thus, this thesis presents a new type of multi-faceted account of borderland development in which ethno-religious considerations came to inform a somewhat messy production of sovereignty in the context of the modernizing transition between empire and nation-state.