2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/11866Gravitational Lensing is an efficient tool to probe: the mass distribution of collapsed systems: galaxies and clusters; high redshift objects thanks to the gravitational amplification; and the geometry of the Universe. I will review here some important aspects of lensing and related issues in observational cosmology.10 pages LaTeX using sprocl.sty. To appear in the 12 th Postdam Cosmology Workshop, "Large Scale Structure: Tracks and Traces", World Scientific 1998Astrophysicstext