  In this paper we first give a short overview of the MACRO detector, which was
operational at the Gran Sasso Laboratory from 1989 till 2000. Then we present
and discuss the results on atmospheric neutrino oscillations, concerning medium
(~4 GeV) and high (~50 GeV) energy data. Using the Multiple Coulomb Scattering
of muons inside the lower part of the detector, estimates of neutrino energies
were made for the high energy sample. The MACRO data, angular distributions,
absolute flux and L/E_nu distributions favour nu_mu <--> nu_tau oscillations
with maximal mixing and Dm^2=2.5 x 10^-3 eV^2.
