Neutrino Masses and Mixings: Status and Prospects

Neutrino oscillations have been found in experiments observing solar and atmospheric neutrinos. They were confirmed by experiments using neutrinos produced by reactors and accelerators. These observations imply that neutrinos have nonzero masses and that the flavor states are superpositions of mass states through a mixing matrix. Indeed, the observed oscillations have revealed two distinct mass differences and two large mixing angles. In this article we discuss these discoveries, the emerging neutrino standard model, the present knowledge of the neutrino masses and mixing parameters, and the prospects for improving upon this knowledge.