I am motivated by answering the age-old question, “Are we alone in the universe?” To this end, my research group models the planetary atmospheres of potentially habitable terrestrial planets both within and outside our solar system. We also test and improve observational predictions against the theories and hypotheses inferred from our atmospheric models. I expect major advances in the coming years, including atmospheric observations of terrestrial exoplanets orbiting main-sequence stars and a search for life on worlds such as Mars and Titan. Our work combines several disciplines, including atmospheric science, astronomy, physics, geology, and biology. Recent work has focused on Mars paleoclimate, expanding and improving definitions of the habitable zone, atmospheric escape processes, and atmospheric-magma ocean evolution.