contoured feedhorns. The first year of SPTpol observing was used to survey a 100-square-degree field centered at R.A. 23h30m declination −55d. The next four years were primarily spent surveying a 500-square-degree region of which the original 100 square degrees is a subset. These are currently the deepest high-resolution maps of the millimeter-wave sky over more than a few square degrees, with the noise level at 150 GHz around 5 micro-Kelvin-arcminute and square root of two deeper on the 100-square-degree field. The SPT-3G camera In January 2017, the third-generation camera SPT-3G was installed on the SPT. Taking advantage of a combination of improvements to the optical system (providing a significantly larger diffraction-limited field of view) and new detector technology (enabling detectors in multiple observing bands in a single pixel), the SPT-3G detector array contains over ten times more sensors than SPTpol, translating almost directly into a tenfold increase in the speed with which the telescope and camera can map a patch of sky to a given noise level. The camera consists of over 16,000 detectors, split evenly between 90, 150, and 220 GHz. In 2018, a new survey began using the SPT-3G camera. This survey was to cover 1500 square degrees to a depth of < 3 micro-Kelvin-arcminute at 150 GHz. Significantly, this field overlaps completely with the BICEP Array observing field, enabling joint analyses of SPT and BICEP data which will deliver significantly better constraints on a potential signal from primordial gravitational waves than either instrument can provide alone. Science goals and results The first key project for the SPT, completed in October 2011, was a 2500-square degree survey to search for clusters of galaxies using the Sunyaev–Zel'dovich effect, a distortion of the cosmic microwave background radiation (CMB) due to interactions between CMB photons and the Intracluster medium in galaxy clusters. The survey has found hundreds of clusters of galaxies over an extremely wide redshift range. When combined with accurate redshifts and mass estimates for the clusters, this survey will place interesting constraints on the dark energy equation of state. Data from the SPT-SZ survey have also been used to make the most sensitive existing measurements of the CMB power spectrum at angular scales smaller than roughly 5 arcminutes (multipole number larger than 2000) and to discover a population of distant, gravitationally lensed dusty, star-forming galaxies. Data from the SPTpol camera was used to make several groundbreaking measurements, including the