Nuclear energy holds the promise to provide vast amounts of reliable baseline electricity at commercially competitive costs with modest environmental impact. However, the future of nuclear energy lies beyond the current generation of light water reactors. Future reactors will be expected to provide additional improvements in safety, maintain high reliability, use uranium resources more efficiently, and produce lower volumes of less toxic solid wastes. Several advanced reactor concepts are under development to meet these demands. In most cases, these designs translate into higher operating temperatures and longer lifetimes, more corrosive environments, and higher radiation fields in which materials must reliably perform. This issue focuses on the materials challenges that will determine the feasibility of these advanced concepts and define the long-term future of nuclear power.