Linked from
The 43 pages that link to Neutrino oscillation, each with the reason it gives.
NeutrinoRelated: Oscillation shows that neutrinos have mass and that flavor states mix.
Lepton numberRelated: Oscillations showed that individual lepton flavors are not conserved exactly.
Yukawa interactionRelated: Oscillations establish neutrino mass, whose Yukawa origin is unknown.
Muon neutrinoRelated: A muon neutrino can later be detected as an electron or tau neutrino.
Electron neutrinoRelated: It allows an electron neutrino to arrive as a different flavor.