CMB-S4 will use telescopes installed at the South Pole to survey the sky. Shown here is the South Pole Telescope. Teams supporting the South Pole Telescope, Atacama Cosmology Telescope, BICEP/Keck and POLARBEAR/Simons Array experiments in Chile and at the South Pole expect to join together to be part of the CMB-S4 collaboration. Photo: Brad Benson