The theoretical and experimental bases of neutrino mass and mixing are reviewed. A brief chronological evolution of the weak interactions, the electroweak Standard Model, and neutrinos is presented. Dirac and Majorana mass terms are explained as well as models such as the seesaw mechanism. Schemes for two, three and four neutrino mixings are presented.

Lectures presented by Paul Langacker at the 11th Mexican School of Particles and Fields, Xalapa, Ver., Mexico, August 2004 (33 pages)