Cosmological Microlensing

. Variability in gravitationally lensed quasars can be due to intrinsic fluctuations of the quasar or due to “microlensing” by compact objects along the line of sight. If disentangled from each other, microlens-induced variability can be used to study two cosmological issues of great interest, the size and brightness profile of quasars on one hand, and the distribution of compact (dark) matter along the line of sight. In particular, multi-waveband observations are useful for this goal. this review Comparison with simulations will show “where we stand”. will questions conclusion/outlook.