  I review the evidence from clusters and groups of galaxies for `relic'
evidence of the high redshift universe. Contrary to the received wisdom,
clusters are old. Their x-ray emitting intergalactic medium in massive clusters
is a reservoir of metal and energy injection from the main epoch of star
formation. There are strong indications that non-gravitational energy was
extremely important in the formation of low-mass clusters and groups, implying
that gravity did not dominate the process on all scales below that of massive,
rich clusters. The data indicate that most of the metals in the universe are
not in stars but in the hot gas and thus the use of stars to trace metal
formation and evolution misses most of the processed material. The group data
shows that galaxies are very poor tracers of mass on the scale of 10^13 M_Sun
and since groups are the `average' place in the universe this probably holds
for most of the visible universe.
