X-ray and optical observations of quadruply lensed quasars can provide a micro-arcsecond probe of the lensed quasar, corresponding to scale sizes of ~10^2-10^4 gravitational radii of the central black hole. This high angular resolution is achieved by taking advantage of microlensing by stars in the lensing galaxy. I will discuss X-ray observations of ten lensed quasars recorded with the Chandra X-ray Observatory as well as corresponding optical data obtained with either the Hubble Space Telescope or ground-based telescopes. These were analyzed in a systematic and uniform way with emphasis on the flux-ratio anomalies that are found relative to the predictions of smooth lens models. A comparison of the flux ratio anomalies between the X-ray and optical bands allows us to conclude that the optical emission regions of the lensed quasars are typically larger than expected from basic thin disk models by factors of ~3-30. I will also discuss how these same flux-ratio anomalies can be used to determine the amount of dark matter in the lensing galaxy.