International cooperation in arbovirus research became increasingly prominent shortly after it was found in the early 1940's, that antigenic relationships existed among certain viruses isolated in different areas of thw world. The interest of a number of scientists and of a private organization led to the establishment of an international information exchange and to the preparation of an international catalogue of arboviruses including certain other viruses of vertebrates. International cooperation was fostered by the interest taken in these agents by the World Health Organization and the creation by this agency of an international net of collaborating laboratories with assigned areas of the world. A number of recent problems have been revealed and solved, or partly solved by this international effort, among which are questions relating to: the Marburg agent disease, the existence of an antigenic relationship between rabies virus and some arboviruses, aspects of the ecology or viruses in the California, Uukuniemi and Kemerovo groups, as well as several unanticipated antigenic relationships among viruses. Numerous questions still remain the solution of which might be expedited by continued and increased cooperative international effort such as overwintering or survival of viruses under unfavorable circumstances, pathogenic potential for man and domestic animals of certain viruses, role on chronic illnesses, establishment of the etiology of certain diseases and investigations of the basic properties of viruses, particularly of the Bunyaviridae.