Abstract: I will discuss the power of new observations of variable black holes (supermassive and stellar mass systems) to probe their growth and evolution. I will touch on our Milky Way’s black hole Sgr A*, the Virgo cluster’s M87, changing-look quasars, the multitude of systems now being discovered by LIGO/Virgo, and briefly explore how we can continue to push this frontier with a new generation of observatories.