Gravitational Lensing offers a unique tool to investigate the total mass distribution in galaxy Clusters as well as the high redshift Universe lensed by the cluster itself. Strong lensing features, as multiple images and distorted arcs, are used to constrain the mass distribution in the inner region of galaxy clusters. Moreover, taking advantage of the high magnification in the strong lensing regime, sources at very high redshift (z>6) can be detected, allowing the investigation of the galaxy population of the early Universe.