Through parliamentary and archival materials, international treaties and academic works, the authors examine the legal rules and institutional structures of the demilitarisation regime. In this process they reassess core concepts of international law and international affairs, such as sovereignty and security, and introduce a theoretical view on the empirical case study of the Åland Islands. The book covers legal, political and policy discursive aspects of demilitarisation, international co-operation, defence and security matters around the Baltic Sea with a broader European and global relevance. It can be a source of inspiration for all those in search of constructive efforts that can address territorial disputes and security challenges.