Meutron radiation embrittlement of nuclear reactor vessels continues to be a major concern of the USNRC. Research is sponsored for improving understanding of radiation embrittlement effects to predict margins of safety and to improve regulations. Regulatory issues that are affected by neutron embrittlement are examined and related to NRC research. Factors that control radiation embrittlement are examined. A comprehensive collection of radiation embrittlement data from surveillance reports and other published reports has been compiled in a computerized data base (PR-EDB). Fracture toughness data for irradiated pressure vessel steel has provided the basis for crack initiation and crack arrest toughness curves. Work is in place to improve our ability to predict thermal annealing recovery and reembrittlement. Areas where additional data are needed are described.