2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/2511Many different families of mass models are used in modern applications of strong gravitational lensing. I review a wide range of popular models, with two points of emphasis: (1) a discussion of strategies for building models suited to a particular lensing problem; and (2) a summary of technical results for a canonical set of models. All of the models reviewed here are included in publicly-available lensing software called gravlens.17 pages, AAS LaTeX; revised version has some new models and more analytic results; the accompanying software is available at http://cfa-www.harvard.edu/castlesAstrophysicstext