Abstract
Massive black hole binaries are one of the most interesting classes of sources that could be detectable by LISA, as they allow tests of general relativity in strong-field conditions and to probe into the very centre of galactic nuclei. We review our present knowledge about the scenario that leads to the formation of these systems and the event rate of detectable gravitational wave signals. We also discuss the use of a LISA-observation catalogue to gain information on the mass - redshift distribution of sources.