The Imaging UltraViolet Spectrograph (IUVS) is the sole planetary remote sensing instrument on the Mars Atmosphere and Volatile Evolution mission (MAVEN). Building on the NASA and ESA legacy of prior UV spectrographs and visible imagers, IUVS has contributed many discoveries by virtue of unique instrument capabilities, observing modes tailored to multiple science goals, and nearly non-stop observations. The overarching goal is to understand Mars’ multiple atmospheric layers, the coupling between them, and their response to external drivers. New insights span every region of the Mars atmosphere, from polar ozone near the surface to escaping hydrogen many planetary radii away. In between, IUVS offers new insights on cloud formation, meteor ablation, nightglow, waves & tides, photochemical escape, Mars D/H and long-term atmospheric evolution. One of the most profound sets of discoveries relates to auroral processes on Mars. Aurora were expected to differ from Earth’s due to Mars’ lack of a global magnetic field, but unexpected IUVS results are offering a new paradigm for stellar influences on non-magnetized planets. This paradigm shift could have implications beyond the solar system for billions of extrasolar planets which may or may not have global magnetic fields.