The Catalina Real-time Transient Survey covers 80% of the sky to a magnitude limit of V~20 and has light curves for 500 million objects with typically 250 observations over a baseline of almost ten years. It is an unprecedented data set for understanding the temporal behaviour of many classes of astrophysical phenomena. It also serves as an excellent testbed on which to develop the tools and techniques necessary to work with future data intensive projects such as LSST and SKA. In this talk, I will review what CRTS is telling us about the variable sky and particularly how it is providing new insights into the physics of quasars.