In Europe, species and ecosystems struggle to cope with severe human pressures in heavily fragmented landscapes extending across a large number of comparatively small states. This makes the conservation of European biodiversity a challenging enterprise, and the need for transboundary cooperation particularly great. This chapter introduces and analyzes the two principal international legal regimes aimed at the conservation of biological diversity in Europe at a transboundary level. The first of these is the Council of Europe’s Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention) of 1979. The second regime is composed by two legal instruments of the European Union (EU), the Directive on the Conservation of Wild Birds (Birds Directive) of 1979 and the Directive on the Conservation of Natural Habitats and of Wild Fauna and Flora (Habitats Directive) of 1992. Particular emphasis is given to those features which set these instruments apart from other global and regional nature conservation regimes.