Why are some non-state actors more successful than others in developing and maintaining durable patterns of transnational interaction? Why are some transnational actors more successful in their lobbying than others? Many non-governmental organizations today have regular contacts with counterparts in other littoral states. In some cases, the non-state actors have also deepened their cooperation and established regional international non-governmental organizations or transnational networks. Their purpose has been, amongst other things, to establish a platform from which they can interact with the Baltic Sea states and influence regional intergovernmental processes. In explaining these patterns of transnational relations, the author highlights a broad range of conditions relating to the actors themselves as well as to structure.