Materials for future nuclear energy systems must operate under more extreme conditions than those in current Gen II or Gen III systems. These conditions include higher temperature, higher dpa, and more corrosive environments. This paper reviews some of the fuels and structural materials used in advanced nuclear energy systems and identifies promising candidates for these systems. Fuel systems includes metallic fuels for the sodium cooled reactor, TRISO-coated particle fuel for the high temperature gas reactor, molten salt reactor fuels, and accident tolerant fuels for light water reactors. Structural materials applications include the sodium fast reactor, lead fast reactor, high temperature gas reactor, molten salt reactor and extended life light water reactors. A final section focuses on plasma-facing and blanket materials for deuterium-tritium fusion reactors. (C) 2019 Elsevier B.V. All rights reserved.