Mass Spectrum and the Nature of Neutrinos

Taking as input the best fit solar neutrino anomaly description, MSW LMA, and the tritium beta decay results we estimate the allowed range of neutrino masses independently of their nature. Adding the present bound on the effective neutrino mass coming from neutrinoless double beta decay, we narrow this range for Majorana neutrinos. We complete the discussion by considering future perspectives on determining the neutrino masses, when the oscillation data will be improved and the next experiments on $(\beta\beta)_{0\nu}$ and $^3H$ decay give new bounds or obtain concrete life-times or distortions in the energy distribution.