Gravitational Lensing - A brief review

Gravitational lensing has established itself as a valuable tool in many astrophysical fields in the roughly 20 years of its existence as an observational science. In this brief review, first the basics of lensing are introduced. Then it is shown that the two propagation effects, gravitational lensing and interstellar scintillation, have a number of properties in common. Finally, various lensing phenomena are discussed with emphasis on recent observations.