  The total energy emitted by the growth of massive black holes is large and
can be 10-50 per cent of that emitted by stars in the universe. I show how the
X-ray Background provides a good measure of this energy and also why most
accretion power is absorbed and re-emitted in the far infrared band. A model
for the obscured growth of massive black holes is presented which accounts for
both the high absorption and the observed black hole to galaxy spheroid mass
correlation. Future missions should detect the obscured X-ray sources
associated with the growth of massive black holes.
