Observations of Cluster Evolution at High Redshifts and Cosmological Measurements

I will review the evidence from ROSAT, Chandra, and XMM observations of distant clusters for significant evolution in the cluster population by z=0.5. The evolution is evident in the changing scaling relations and decreasing cluster number density at a fixed luminosity, temperature, or mass. The rate of the cluster evolution can be used to determine the growth factor of the density perturbations at z=0.5-1, and thus estimate the cosmological parameters. Most of the recent results on (Ω,Λ) based on cluster evolution intersect with the CMB and Sn Ia constraints near the ``standard parameters'', Ω_m=0.3 and Λ=0.7. New, high accuracy cluster evolution data allows also the independent estimate of the equation of state parameter for the dark energy.