first detection of the so-called "B-mode" or "curl" component of the polarized CMB. This B-mode signal is generated at small angular scales by the gravitational lensing of the much larger primordial "E-mode" polarization signal (generated by scalar density perturbations at the time the CMB was emitted) and at large angular scales by the interaction of the CMB with a background of gravitational waves produced during the epoch of inflation. Measurements of the large-scale B-mode signal have the potential to constrain the energy scale of inflation, thus probing the physics of the universe at the earliest times and highest energy scales imaginable, but these measurements are limited by contamination from the lensing B modes. Using the larger E-mode component of the polarization and measurements of the CMB lensing potential, an estimate can be made of the lensing B modes and used to clean the large-scale measurements. This B-mode delensing was first demonstrated using SPTpol data. SPTpol data also has been used to make the most precise measurements of the E-mode power spectrum and temperature-E-mode correlation spectrum of the CMB and to make high-signal-to-noise maps of the projected matter density using reconstructions of the CMB lensing potential. The 1500-square-degree SPT-3G survey will be used to achieve multiple science goals, including unprecedented constraints on a background of primordial gravitational waves joint analysis of B-mode polarization with the BICEP Array, a unique sample of distant galaxy clusters for cosmological and cluster evolution studies, and constraints on fundamental physics such as the mass of the neutrinos and the existence of light relic particles in the early Universe. The Atacama Cosmology Telescope has similar, but complementary, science objectives. Funding The South Pole Telescope is funded through the National Science Foundation Office of Polar Programs and the United States Department of Energy, with additional support from the Kavli Foundation and the Gordon and Betty Moore Foundation. Funding for the SPTpol and SPT-3G instruments and operations are also provided by the United States Department of Energy Office of Science, Office of High Energy Physics. Operations On , the South Pole Telescope achieved first light. Formal science observations began in March 2007. Commissioning observations and an initial small survey were completed during austral winter 2007 with winter-overs Stephen Padin and Zak Staniszewski at its helm. In 2008, larger survey fields were completed with winter-overs Keith Vanderlinde and Dana Hrubes, and in 2009 with winter-overs Erik Shirokoff and Ross Williamson.