Abstract

Quasar lensing offers an important diagnostic of masses and mass distributions in foreground objects, and is sensitive to both baryonic and dark matter. In addition, strong lensing also magnifies the brightness of background objects, allowing one to probe regions with potentially interesting cosmological information. In this review I present individual theoretical results, and discuss possible future applications of quasar lensing, and the observational programmes which will develop the subject in the coming years.