Experiments in underground laboratories have shown strong evidence of physics beyond the standard model. The anomalies observed in electron-neutrinos from the sun and muon-neutrinos from cosmic rays interactions in the atmosphere can be explained if neutrino are massive and oscillate. After an introduction of the basic concepts of the new neutrino physics, the status of the experimental evidence will be reviewed.
The Gran Sasso Laboratory has given important contributions to the establishment of both anomalies. We are now defining the physics program for the next phase, focussing on neutrino physics with a complementary set of experiments on the muon-neutrino beam from CERN (CNGS project), on solar neutrinos, on atmospheric neutrinos and on neutrinos from supernova explosion. The relevant thermonuclear cross-sections will be measured. The Majorana vs. Dirac nature of electron neutrinos will be explored with the search for neutrino-less double beta decays in different isotopes.