The Standard Model of the fundamental constituents of nature requires that a tau neutrino exists to be the partner of the tau lepton discovered 25 years ago at SLAC. The definitive proof of the existence of a neutrino has always been to observe its interaction with matter and determine the identity of the lepton produced. The DONUT (Direct Observation of NU Tau) experiment used a Fermilab high energy proton beam to produce neutrinos and then detected the interaction of those neutrinos producing tau leptons. This talk will describe the experiment, its difficulties, and its success.