In the decades around 1900, there was a real boom in the establishment of nongovernmental international organizations in Europe. Their congresses debated a wide range of scientific, political, and social problems that had arisen with the industrial development and the dynamics of internationalization since the 1880s. The elites that were engaged in the meetings of international organizations, reacted to sociopolitical or economic change and developed new concepts for societal reform. The nation remained central to the world views of these elites and to the professional or political careers of their members. Internationalism and nationalism were closely linked in the decades before World War I. This shaped also their relations with national governments, the concrete forms of internal cooperation of international associations, and even the specific sociability of the transnational meetings of the elites. The contributions in this volume deal with the elites and encounters of various types of international organizations.