I will review scenarios for the assembly of massive
black holes (MBHs) that trace their hierarchical build-
up far up in the dark halo merger tree. The first active
galactic nuclei may have formed 200 Myr after the big
bang in one million solar mass halos. I will discuss
the conditions under which MBHs become
incorporated through a series of mergers into larger
and larger halos, sink to the center owing to
dynamical friction, accrete a fraction of the gas in the
merger remnant to become supermassive, form a
binary system, and eventually coalesce. The spin
distribution of MBHs is determined by gas accretion,
and is predicted to be heavily skewed towards fast-
rotating Kerr holes, already in place at early epochs,
and not to change significantly below redshift 5.
Decaying MBH binaries will eject hypervelocity stars,
shape the innermost central parsec of galaxies, and
should be detected in significant numbers by LISA.