A general classification of three-neutrino models and Ue3

A classification of models with three light neutrinos is given. This classification includes virtually all of the three-neutrino models proposed in the last few years, of which there are approximately one hundred. The essential ideas, attractive features, and characteristic problems of the different classes of model are discussed. The classification is based principally on how large νμ-ντ mixing is obtained. A general discussion of the mixing parameter Ue3 is then given, showing what values are to be expected for it in each type of model