[en] The resources of international co-operation, notably through the Nuclear Energy Agency, can substantially help 'keep the nuclear option open' in a sustainable development perspective, for example by helping preserve and develop scientific and technical know-how, maintaining adequate human resources both in quantity and quality, contributing to greater cost-effectiveness of nuclear operations, and improving stakeholder confidence in radioactive waste management solutions. The 1999 Annual Report of the Nuclear Energy Agency illustrates various facets of the international co-operation made available to Member governments which assists them in rising to these challenges: Nuclear Development and the Fuel Cycle, Nuclear Safety and Regulation, Radiation Protection, Radioactive Waste Management, Nuclear Science, Data Banks, Legal Affairs, Joint Projects and Other Co-operative Projects. (author)