Galaxy/ X-ray/ Dark Matter Clusters: Laboratories 
              for Galaxy Formation and Cosmology

          A.E. Evrard (Physics Department, U. Michigan)

Clusters of galaxies mark the massive tip of the hierarchy of
collapsed, (quasi-)equilibrium structures in our universe.  The
structure and content of their visible components result from the
interplay of complex dynamical, thermodynamical and chemical
activities driven by gravity, radiative cooling and star formation.
In the limit of the most massive clusters, however, observational and
computational evidence points to a relatively simple picture in which
galaxy formation is inefficient and the intracluster medium (ICM)
structure is largely controlled by gravitationally-induced shock
heating.  I will show that numerical experiments incorporating gravity
and an approximate treatment of galaxy feedback are capable of
reproducing the observed statistical properties of ICM bulk structure
at the $10-20%$ level.  The models predict new X-ray spatial and
spectral features that are now observable by the Chandra and XMM
satellites.  I will discuss the expected evolution of visible cluster
properties with redshift, point out the limitations involved in using
observations of a few distant clusters to constrain cosmological
parameters, and outline advances to be expected from the next
generation of wide-field surveys at optical, sub-mm and X-ray
wavelengths.