This chapter assesses cooperation and conflict in diplomacy and war in and around Central Europe. Cooperation and conflict are among the most distinctive themes in the history of pre-modern Central Europe, forms of socio-political and cultural interplay that shaped the developments of small- and large-scale polities between the decline of the Classical Roman Empire and the emergence of the nation state in Modern times. The various forms and extent of cooperation and conflict in Central Europe relate to a diversity of ethnicities, political identities, traditions, religions, and cultural differences which still have political consequences today. Yet while the region was densely populated and economically interconnected, emerging conflicts rooted in, at time, the troublesome organization of coexistence, were resolved through a vast range of means that extended from consensual diplomacy to articulated war. The chapter then reviews the forms of Christianity and relations its processes formatted in the Slavic Balkans; discusses dynastic attitudes to the crown in medieval Poland; looks at approaches to religious controversies, such as the Hussites; and considers the processes of separation, interconnectedness, and othering in the Slavic East.