  The relationship between galaxies and supermassive black holes (SMBH) found
in their cores plays a key role in the formation and evolution of both of these
major constituents of the universe, as well as the evolution of the
intergalactic medium. Neither can be fully understood on their own, and studies
of galaxy and SMBH co-formation and co-evolution are now among the central
topics of research in cosmology. Yet the very origins, and the early growth
phases of the SMBH are still not firmly established. We review our current
understanding of the relevant processes and their astrophysical and
cosmological context, with an emphasis on the observability of the SMBH growth
mechanisms at high redshifts, and their leftover progeny at low redshifts.
