I review some aspects concerning the physics of neutrino mixing and
oscillations. I discuss in some detail the physical neutrino oscillations
parameter space in the case of two and three family mixing, and briefly
describe the current knowledge of neutrino mixing parameters according to the
present solar, atmospheric, and reactor neutrino data. I also briefly comment
on the possibility of solving the LNSD anomaly together with the solar and
atmospheric ones. I conclude by emphasising that that even though in five to
ten years time a lot will be learnt from the next round of neutrino
experiments, a great deal about neutrino masses and neutrino mixing will remain
unknown.Comment: Invited Plenary Talk at the NUFACT'01 Conference, 14 pages, 2 figure