Neutrino Masses and Anomalous Interactions

The interplay between neutrino masses and the interactions of neutrinos with matter is discussed with an eye to extending the latter to include possible new interactions. This conjecture may resolve the conundrum posed by the present experimental data on neutrino oscillations which suggest the existence of four neutrinos, whereas Z decay and Big Bang Nucleosynthesis allow only three. The case of a possible sterile neutrino is also briefly discussed.