  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.
