Nuclear power is an important source of primary energy for electricity generation worldwide. More than one sixth of the world electricity requirement is met by nuclear power plants; this share is approximately 24% in the OECD countries. While existing plants play an important role in power supply today, a number of questions with important consequences for the future still need to be answered. They include the management of nuclear waste. the structural reshuffle of the nuclear industry, and the deregulation of the electricity supply sector as major administrative problems. Another aspect are the future requirements to be met by nuclear power plants, and in their operation, resulting from the increasing age of the existing nuclear power plant park. The concept of plant Life Management (PLIM) is considered an important contribution to the future operation of existing plants accompanied by the continuous further development of safety and economic performance. Activities in different countries have Brown to different stages of development as far as the operating life of nuclear power plants is concerned. In the United States, for instance, permits are now issued for plant operation beyond the forty years covered by the first permits. In Japan, strategies of PLIM are being worked out on the basis of sixty years of plant life while, in other countries, similar approaches have reached advanced stages of development in some cases or are still under development in others.