2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/3809I show how weak gravitational lensing can be used to image the 3-D mass distribution in the Universe. An inverse relation to the lensing equation, relating the lensing potential evaluated at each source to the full 3-D Newtonian potential, is derived. I consider the normal modes of the lensing problem and clarify the equations using a small-angle approximation. Finally I consider the prospects of using this method to estimate the 3-D matter distribution from a realistic galaxy lensing survey.4 pages, RevTex, submitted to Phys. Rev. LettAstrophysicstext