  The theoretical basics of neutrino mass and mixing are reviewed. Dirac and
Majorana masses are explained, and added together to produce the see-saw
picture of the lightness of neutrinos. This picture predicts that neutrinos are
Majorana particles. The character, and an apparent paradox, of Majorana
neutrinos are examined. The physics of neutrino flavor change (oscillation), in
vacuo and in matter, is reviewed.
