  After exactly a century since the formulation of the general theory of
relativity, the phenomenon of gravitational lensing is still an extremely
powerful method for investigating in astrophysics and cosmology. Indeed, it is
adopted to study the distribution of the stellar component in the Milky Way, to
study dark matter and dark energy on very large scales and even to discover
exoplanets. Moreover, thanks to technological developments, it will allow the
measure of the physical parameters (mass, angular momentum and electric charge)
of supermassive black holes in the center of ours and nearby galaxies.
