The U.S. National Science Foundation (NSF) was established in 1950. Since that time it has continuously advanced its methods for evaluation at all levels: evaluation of proposals submitted to fund the work of individual researchers, groups of researchers and major centers; evaluation of NSF internal programs; evaluation of NSF internal administrative directorates; and evaluation of the NSF as a whole. The NSF evaluation systems rely heavily on the knowledge, skills and abilities of individuals who are expert in the subject matter or organization being reviewed, and who volunteer their time as a part of their service to the research community to improve the health of science.