The Atacama Cosmology Telescope (ACT) is a six-meter diameter telescope on Cerro Toco in the Atacama Desert of northern Chile (image above by Jon Ward). It is designed to make high-resolution measurements of the cosmic microwave background (CMB) temperature and polarization anisotropies and detect massive galaxy clusters via the thermal Sunyaev Zel'dovich (tSZ) effect. Reconstruction of the CMB lensing potential will play a key role in the cosmological detection of neutrino mass, and measuring the imprint of primordial gravitational waves in B-mode polarization could provide unique insights into the early universe and quantum nature of gravity. The DR4 products use data collected from 2013-16 but also includes data collected from 2008-10. DR5 adds ACT data acquired in 2017-18 in frequency bands centered at 98, 150 and 220 GHz.