Kaaret's main interest is understanding the intense gravitational fields surrounding black holes and neutron stars and the dynamics of the accretion of matter onto these objects. He conducts observations at X-ray, optical, and radio wavelengths of objects in our Milky Way galaxy and in external galaxies. His current work concerns the highly luminous X-ray sources in nearby galaxies which have been interpreted as being intermediate-mass or "medium-sized" black holes, jet ejection from black holes, and the properties of X-ray binaries in the early universe. He also builds instrumentation for space-based X-ray astronomy and ground-based gamma-ray astronomy.