Tobias Marriage’s research interests lie in cosmology and astrophysics with an emphasis on the cosmic microwave background (CMB). His research activities include millimeter-wave instrumentation, fieldwork, and analysis. Marriage played a major part in building the Atacama Cosmology Telescope (ACT), a mm-wave telescope 5,000 meters above sea level in Chile that studies fine angular-scale structure in the CMB. He and his group continue to work with ACT data and other datasets to study galaxies and galaxy clusters. Marriage is now a Co-PI of the Cosmology Large Angular Scale Surveyor (CLASS) project. CLASS is an array of telescopes designed to measure the CMB polarization on the largest angular scales over a broad range of frequencies. The primary goal of CLASS is to detect and characterize the expected gravitational waves from inflation via the induced B-mode polarization pattern in the CMB. CLASS also measures when the first stars formed (by constraining the optical depth to reionization) and searches for large angular scale polarization anomalies that could provide new insights beyond the current cosmological paradigm.