The cosmic microwave background (CMB) provides a unique window into early universe physics. The CMB is generated by well-understood dynamics that enables precise calculation of its observable features which directly connects new measurements to fundamental physics. I will discuss the latest cosmology constraints from the South Pole Telescope (SPT), including the first detection of a curl-only component (B-modes) in the polarization of the CMB by SPTpol. I will describe the instrumentation and detector technology in development for next-generation experiments, including SPT's next camera, SPT-3G, and a future ground-based CMB experiment, CMB-S4. The science goals of these experiments aim to answer some of the most exciting questions in cosmology: to differentiate between dark energy and modified gravity to explain the origin of cosmic acceleration, to test and constrain physics at grand-unified theory energy scales (~1e16 GeV), to measure the sum of the neutrino masses at a level below the minimum mass expected from neutrino oscillations (<0.06 eV), and to precisely constrain the relativistic energy density of the universe and any "dark radiation" component.