Models of Neutrino Mass and Mixing

There are two basic theoretical approaches to obtaining neutrino mass and mixing. In the minimalist approach, one adds just enough new stuff to the Minimal Standard Model to get $m_{\nu }\mathrm{\ne }0$ and $U_{\alpha i}\mathrm{\ne }1$. In the holistic approach, one uses a general framework or principle to enlarge the Minimal Standard Model such that, among other things, $m_{\nu }\mathrm{\ne }0$ and $U_{\alpha i}\mathrm{\ne }1$. In both cases, there are important side effects besides neutrino oscillations. I discuss a number of examples, including the possibility of leptogenesis from R parity nonconservation in supersymmetry.