  The role of X-ray observations for cosmological studies and conclusions is
briefly explored. X-rays currently yield cosmologically interesting results on
the abundances, evolution and gas content of clusters of galaxies, on the
clustering and evolution of active galaxies and on the X-ray Background. They
are unlikely in the long term future to give the most precise values of the
cosmological parameters, although in the short term the baryon fraction of
clusters and the Sunyaev-Zeldovich effect will remain important determinants
and checks for some parameters. X-rays will however continue to play an
important role in studying the astrophysics of the formation and growth of
black holes, galaxies, groups and clusters. It is possible that this role will
be crucial, if winds from active galaxies are responsible for breaking the
simple gravitational scaling laws for clusters.
