The phenomena of massive neutrinos are discussed. The neutrino oscillation and the electromagnetic properties of neutrinos are considered. First we described the mass terms in Lagrangian for Dirac, Majorana, and Dirac-Majorana neutrinos. The probabilities of neutrino oscillation are derived and their properties are discussed. Also the resonant amplification of oscillation in matter(MSW) is considered.
The electromagentic properties show different aspects for Dirac and Majorana neutrinos. If a neutrino has a magnetic moment, there is a precession of spin or spin-flavor when it propagates in the magnetic field. There is also a resonant effect of the precession in matter like MSW effect. The discussions about the mass and the mixing matrix of leptons based on the results of recent neutrino oscillation experiments are reviewed.