  Ultraluminous X-ray sources (ULXs), first observed ~30 years ago, have been
argued as extreme stellar mass black hole binaries or a new class intermediate
mass black hole. In order to settle this debate, scientists have utilised a
wide range of telescopes, exploiting large sections of the electro-magnetic
spectrum. Here we review some of the insight gained from these observational
studies, collating an overview of our current position in ULX research.
