This study of the development of international data networks, a phenomena of the 1970's, and policy issues arising from their use is an in depth investigation of 24 private and six public European networks commissioned from Logica Limited and sponsored by the governments of France, Germany, the Netherlands, Norway, Spain, and Sweden. The report discusses reasons for using international data networks, describes their technological development, investigates transborder applications, presents access control and security problems and their solutions, and analyzes the costs and economics of international networks. The 27 conclusions presented range from the benefits of international data transmission to the participating companies, the involved nations, and the scientific research community to the developing international implications of mutual interdependence, and to the impact of costs on multinational corporations and smaller local users. Predicting that an European public network will be unavailable for at least five years, the report recommends that private networks receive preferential tariff treatment to meet the existing need of such a network. The appendices include descriptions of the 30 networks investigated, with diagrams, a checklist of information to be sought, the questionnaire used, and a checklist of information in network description. (RAO)