Neutrino mass and oscillations

Important recent discoveries in neutrino physics launched a new era in the search for 'physics beyond the Standard Model'. In particular, observation of the zenith angle dependence of the atmospheric neutrino flux, of the difference in the deduced flux of solar neutrinos based of their charged and neutral current interactions, and of the reduction in the flux of reactor antineutrinos at large distances convincingly show that neutrinos are massive and mixed. I briefly review the formalism and physics of the neutrino mass and mixing, and then concentrate on discussion of the KamLAND reactor neutrino experiment. That experiment, a continuation of a long tradition of studies involving neutrinos produced in nuclear reactors, is the first one to observe neutrino oscillations with a man-made and well understood source. I describe the detector, physics of the detection reaction, the determination of the reactor antineutrino flux and, naturally, the results and their implications (Author)