Analysis of oscillations of atmospheric neutrinos

We briefly review the current status of standard oscillations of atmospheri c neutrinos in schemes with two, three, and four flavor mixing. It is shown that, although the pure nu (mu) --> nu (tau) channel provides an excellent 2 nu fit to the data, one cannot exclude, at present, the occurrence of ad ditional sub-leading nu (mu) --> nu (e) oscillations (3 nu schemes) or of s izable nu (mu) --> nu (s) oscillations (4 nu schemes). It is also shown tha t the wide dynamical range of energy and pathlength probed by the Super-Kam iokande experiment puts severe constraints on nonstandard explanations of t he atmospheric neutrino data, with a few notable exceptions.