The 17 keV neutrino

A controversy over the possible existence of a 17 keV mass state coupled to the electron neutrino occurred during the period 1985-1993. A number of independent experiments found evidence for this state in nuclear decay spectra, while others did not. Ultimately a consensus that the 17 keV neutrino does not exist was reached. We review and evaluate the experiments that reported evidence for and against the 17 keV neutrino, and discuss the various issues of experimental systematics that contributed to the development and resolution of the controversy. We attempt to distill the lessons learned from this experience and draw some general conclusions that are relevant to future research.