Flavor changing neutral couplings for leptons

The article reviews the conditions for lepton-flavor conservation in leptonic interactions. The conditions are similar to those developed in the quark sector. For neutrinos the mass eigenstates are unitary superpositions of flavor states which together with small mass differences produce neutrino oscillations. A new property for neutrinos is the fact that their masses are very small suppressing their couplings to neutral scalar fields. The results are demonstrated in several models.