Gravitational lensing is a powerfull tool both to investigate galaxy structure and to determine cosmological parameters. The optical depth and the average timescale of the microlensing events detected towards LMC has been used to constrain the lenses mass function. The pixel lensing technique has been employed to analyze data taken with the MDM and Naini Tal telescopes towards M31 in order to increase the number of events. To study distant galaxies, we have developped a semianalytical method to reconstruct the lens potential in quadruply imaged QSOs. Application to PG1115+080 gives us an estimate of . To take into account the lens models degeneracy, we have elaborated a new semianalytical approach applying it to PG1115+080 and B1422+231. We get .