  The basics of neutrino oscillations is presented. Existing evidences of
neutrino oscillations, obtained in the atmospheric and solar neutrino
experiments, are considered. The new CHOOZ bound on the element $|U_{e3}|^{2}$,
obtained from the three-neutrino analysis of the data, is discussed. Decoupling
of neutrino oscillations in the solar neutrino range of $\Delta m^{2}$ is
considered.
