The idea of neutrino oscillations was suggested in 1957 by B. Pontecorvo. It took more than 40 years and the efforts of many experimental teams before the first convincing evidence that neutrinos are massive and mixed particles came to light. A central figure in this enthusiastic endeavour to unravel neutrino properties has been Samoil M. Bilenky, from his early collaboration (in Dubna) with Pontecorvo to his most recent attempts at analyzing and reconciling, in a coherent theoretical framework, the results of many difficult experiments. These aim at the measurement of neutrino masses and oscillations: from the various solar neutrino experiments, via the LSND accelerator experiment, to the most suggestive atmospheric neutrino experiments. This volume, which celebrates the seventieth birthday of Samoil M. Bilenky, offers a fairly complete overview of theoretical issues and experimental facts about our present understanding of neutrino physics and its implications for astrophysical and cosmological problems. Indeed, some contributions are devoted to more general topics within and beyond the Standard Model, from lattice QCD to dark matter and supersymmetric models.