The tau neutrino or tauon neutrino is a subatomic elementary particle  which has the symbol and no net electric charge. Together with the tau, it forms the third generation of leptons, hence its name tau neutrino. Its existence was immediately implied after the tau particle was detected in a series of experiments between 1974 and 1977 by Martin Lewis Perl with his colleagues at the SLAC–LBL group. The discovery of the tau neutrino was announced in July 2000 by the DONUT collaboration.

A neutrino ( or ) (denoted by the Greek letter ν) is a lepton, an elementary particle with half-integer spin, that interacts only via the weak subatomic force  and gravity. The mass of the neutrino is tiny compared to other subatomic particles. They are the only identified candidate for dark matter, specifically hot dark matter.