The revival of inter- state conflicts and full- scale war in Europe has attracted attention to horizontally and vertically strengthening European defence and security using national, regional, European and Allied frameworks. Although member states of the European Union (EU) have membership in different security organisations and varying attitudes towards neutrality and the struc-turing of the national Armed Forces, the commonality of threats and security interests suggests the necessity of cooperation through new initiatives and already well- established formal frameworks. The case of Norwegian and Swedish defence and security cooperation was chosen for this chapter for a few reasons: the two countries are part of the Nordic regional cooperation initia-tive, and the status of their membership in the EU and NATO are different;1hence, they provide an opportunity to explore the extent of differentiation pro-cesses and dynamics within the sphere of defence and security under the con-ditions of deteriorating strategic environment. The chapter aims to analyse the spectrum of cooperation that already exists between the two countries and the members of the Nordic cooperation initiative with further opportunities for diversification of cooperation and deepening of the scope in the air domain. It illustrates the potential for the regional cooperation even in the more challeng-ing sphere of security and defence. Furthermore, the factors contributing to the success of this collaboration (similar cultural specifics, previous collabora-tive experiences, flexibility of commitments) are discussed in terms of the over-all trends of differentiation and relevant lessons for regional collaborative initiatives in the EU and NATO.