NRC’s approach to ensuring the safety of nuclear power includes two complementary approaches, one more deterministic and one more probabilistic. These two approaches address the uncertainties in the underlying methods and data differently, with each approach having its strengths and limitations.This paper provides some background on the historical evolution of deterministic and probabilistic methods in the regulation of nuclear power plants, describes the Commission’s policy on the use of probabilistic methods to complement the more traditional deterministic approach, and identifies some example challenges as a staff group considers a strategic vision of how the agency should regulate in the future.