2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/4629I present an overview of strong and weak gravitational lensing by galaxy clusters. After briefly introducing the principles of gravitational lensing, I discuss the main lessons learned from lensing on the mass distribution in clusters and their relation to cosmology.Invited Review at "Matter and Energy in Clusters of Galaxies", Taipei 2002 (7 pages, no figures)Astrophysicstext