At the end of 2001, 438 nuclear power reactors were in operation in 31 countries around the world, generating electricity for nearly 1 billion people. They account for approximately 17 percent of worldwide installed base capacity for electricity generation and provide half or more of the electricity in a number of countries. As a whole, these reactors have an excellent operating record and are generating electricity in a reliable, environmentally safe, and affordable manner without emitting noxious gases into the atmosphere. Concerns over energy resource availability, climate change, air quality, and energy security suggest an important role for nuclear power in future energy supplies. While the current Generation II and III nuclear power plant designs provide an economically, technically, and publicly acceptable electricity supply in many markets, further advances in nuclear energy system design can broaden the opportunities for the use of nuclear energy. To explore these opportunities, the U.S. Department of Energy's Office of Nuclear Energy, Science and Technology has engaged governments, industry, and the research community worldwide in a wide-ranging discussion on the development of next-generation nuclear energy systems known as "Generation IV". Generation IV nuclear energy systems will: Provide sustainable energy generation that meets clean air objectives and promotes long-term availability of systems and effective fuel utilization for worldwide energy production. Minimize and manage their nuclear waste and notably reduce the long term stewardship burden in the future, thereby improving protection for the public health and the environment. Increase the assurance that they are a very unattractive and least desirable route for diversion or theft of weapons-usable materials. Excel in safety and reliability. Have a very low likelihood and degree of reactor core damage. Eliminate the need for offsite emergency response. Have a clear life-cycle cost advantage over other energy sources. Have a level of financial risk comparable to other energy projects.