| Abstract: Pulsar Timing Arrays (PTAs) have found compelling evidence for the existence of a Gravitational Wave Background (GWB): a ‘hum’ of low-frequency gravitational waves that permeates the Universe, emitted by the loudest gravitational wave (GW) sources in the Universe: Massive Black Hole Binaries (MBHBs). In gas-rich galactic nuclei, MBHB evolution is expected to be accompanied by interaction with circumbinary accretion disks (CBDs). In this talk I will show that, i) accretion from CBDs increases the amplitude of the GWB, but that CBD-induced orbital expansion has a negligible effect, ii) the mass ratio evolution and `eccentricity attractor' derived from CBD simulations is expected to induce a strong signature in the MBHB population, and that iii) evidence for such a signature has already been found in stellar binaries. Finally, I will discuss how the accretion from CBDs may enable multi-messenger detection of these systems through electromagnetic follow-up, and present preliminary models of the diverse electromagnetic signatures emitted by MBHBs in CBDs. Link to the Event Video |