How, and why, does a cross-border regional civil society come into existence? This book sets out to explore the phenomenon of transnationalization and regionalization of civil society through a case study of cross-border NGO cooperation in the Baltic Sea region. The theoretical ambition is to contribute to a greater understanding of the processes behind the formation of a regional civil society, and to propose a conceptual model that would make such understanding easier. At the same time, at the empirical level, the study sheds light on the context-specific factors that have shaped the mode of civil society regionalization in the Baltic Sea area. In the book, the image of the developing regional civil society as seen through the eyes of the involved actors, is set against the background of the New Regionalist ideas that prevailed among observers of Baltic Sea politics in the early 1990s. The investigation shows that the regional civil society cooperation structures around the Baltic Sea are neither as ‘civil’ – in the sense of being autonomous from the governmental sphere – nor as ‘regional’ as it has often been assumed. More generally, the results of this study indicate that the process of civil society regionalization is not one that will necessarily lead to the emergence of a particularly regional civil society. Rather, it should be seen as a transition phase in a wider process of civil society transnationalization, where the emerging transnational cooperation structures assume the specifically regional shape as long as it is useful in their pursuit of other interests, the region itself being of a secondary importance.