The Pan-European Biological and Landscape Diversity Strategy, endorsed by the 3rd Conference of Ministers "An Environment for Europe" in 1995 in Sofia, aims at ensuring the conservation of ecosystems, habitats, species, their genetic diversity and landscapes of particular interest, through establishing the Pan-European Ecological Network. Transfrontier co-operation represents an essential aspect of the protection of biological and landscape diversity: the conservation of numerous species of fauna and flora is conditioned by their opportunities for distribution and migration in transborder areas, which constitue real ecologial corridors, as well as in stopover areas. The first international Symposium of the Pan-European Ecological Network highlighted ways of promoiting such a transfrontier co-operation.