The 100-year history of the neutrino has given us good reasons to believe that it exists. From the observation of the continuous energy spectrum in decay, to the Reines-Cowan experiment that first directly detected the neutrino, to the recent works on neutrino oscillations, we have seen numerous experiments, consistent with the existence of the neutrino. In each of these experiments the neutrino behaves as though it were a particle with no charge, very small mass, and spin 1/2. We can, then, reasonably conclude that there is such a particle with those properties. 1 As Nancy Cartwright might put it, “If there are no neutrinos, we have no explanation of those experimental results.”