I discuss how to make predictions for the amplitude of the gravitational-wave background (GWB) produced by supermassive black hole (SMBH) binaries and for the event rate of SMBH coalescences within the framework of galaxy formation theory in a cold dark matter (CDM) universe. The former can be detected by pulsar timing arrays (PTAs), while the latter will be probed by LISA. We have developed a...
