The South Pole Telescope survey of 2500 deg^2 in the southern sky has enabled the selection of a large sample of massive galaxy clusters extending to z~1.5 through their Sunyaev-Zel'dovich effect. Dark Energy Survey deep, optical multiband imaging is enabling studies of the galaxy populations within those clusters and constraints on the masses of the systems through weak lensing. Analyses of the population of SZE selected clusters from SPT indicates cosmological constraints that are in good agreement with other cosmological probes and that together with other probes provide among the most precise constraints yet on the growth rate of cosmic structure and the equation of state of the dark energy. Improved mass constraints from weak lensing and new cluster finding experiments in the X-ray through eROSITA promise to open the window on new studies of cosmology and structure evolution.