This dissertation analyses the phenomenon of regionalism around the Baltic and the Black Sea since the end of the Cold War with a comparative approach and from a neorealist point of view. The analysis has as main focus regional organizations, the Council of the Baltic Sea States (CBSS) and the Black Sea Economic Cooperation (BSEC), which define the geographical and political borders of the Baltic and the Black Sea region. These latter are considered international regimes. The three main variables taken into consideration in this study, namely the distribution of power among the big states, the geographical location and the historical legacy, affect both directly and indirectly the relations among the states in each region. This is evident in the four sectors analysed, which are hard security, energy, economic development and environment. While the last three sectors are areas of cooperation within the CBSS and the BSEC, hard security is not. Its inclusion in the study is due to the fact that it strongly affects the power relations among the states in the two regions and that it is strictly linked to the other three sectors. Although the CBSS and the BSEC have established Working Groups ad hoc with the aim to make cooperation working effectively, regional states cooperate to the extent that it brings about advantages to them in terms of relative gains in accordance with the neorealist approach. The analysis has shown that the two regimes created on the Baltic and on the Black Sea are ineffective though the CBSS has managed to create stronger cooperative links among its members than the BSEC.
