I will first discuss the motivation for four neutrino models and the
current constraints on them. The simplest cases of 2 + 2 and 3 + 1
models are excluded by a combination of data on solar, atmospheric,
reactor and accelerator neutrinos. However, alternative models with
CPT violation or five or more neutrinos appear to be allowed by the
data. The possible impact of the MiniBooNE experiment on the viable
models is discussed.