Carina Fian, Evencio Mediavilla

We describe principles of gravitational lensing, macrolensing and microlensing. The physics of Quasars is shortly discussed and then quasar macro- and microlensing by galaxies is described. Own observations consist of photometric observations and spectroscopic observations. We show how from the lensing parameters quantities like the Hubble constant, the mass of the lensing galaxy, the size of the accretion disc and the mass of the supermassive black hole at the center of the quasar can be derived.