Almost 200 changing-look AGN/quasars are currently known showing significant spectroscopic and photometric variability on timescales of months to years. Although initially discovered by serendipity, systematic searches of archival survey data, such as SDSS, Pan-STARRS, and CRTS, have identified such sources in significant numbers. Ongoing time domain sky surveys, such as ZTF, which cover the visible sky every few nights, are enabling real-time monitoring of such objects as they transition between different states of activity. However, the known set of changing-look sources spans a range of luminosity, black hole mass, and Eddington ratio and this suggests that a number of different physical mechanisms may be contributing to the same broad observed phenomenology. X-ray observations may well be the key to distinguishing between different models, particularly if contemporaneous with optical observations. In this talk, I will review the current state of the field, and consider how a joint ZTF-SRG data set will greatly improve our understanding of this phenomenon.