In the last decades, a very important breakthrough has been brought in the
elementary particle physics by the discovery of the phenomenon of the neutrino
oscillations, which has shown neutrino properties beyond the Standard Model.
But a full understanding of the various aspects of the neutrino oscillations is
far to be achieved. In this paper the theoretical background of the neutrino
oscillation phenomenon is described, referring in particular to the
paradigmatic models. Then the various techniques and detectors which studied
neutrinos from different sources are discussed, starting from the pioneering
ones up to the detectors still in operation and to those in preparation. The
physics results are finally presented adopting the same research path which has
crossed this long saga. The problems not yet fixed in this field are discussed,
together with the perspectives of their solutions in the near future