Fermilab Cosmic Physics Center

The gas mass fractions and the distribution in mass and redshift of the galaxy cluster population provide powerful probes of cosmology, constraining the cosmic matter density, the amplitude of the matter power spectrum, properties of dark energy, and the mass of neutrinos, among other parameters. Improvements in cluster data on several fronts have yielded significant gains in the last few years, notably the maturation of weak gravitational lensing as a probe of total mass and

the steady expansion of cluster surveys at all wavelengths. I will review the current state of the two leading cluster cosmology tests, and comment on some of the exiting prospects for the coming years.