In this thesis, a theory of neutrino masses and oscillations is built up in the general case. The work is then restricted to the three-species Dirac case, for which the required parameters, a mass scale and a mixing matrix, are provided by phenomenological solutions and by a new Hierarchial Mass Scheme coupled with both Cabibbo and Hierarchial mixings. The oscillations formalism and hypotheses are then applied to neutrino-electron scattering experiments to be performed at Brookhaven, with neutrino energies ranging from 20 to 270 MeV. The ʋ-e scattering cross-sections, the relevant phenomenological quantities, and the resulting predictions are successively calculated and examined. / Science, Faculty of / Physics and Astronomy, Department of / Graduate