Carbon and sulfur, despite their low bulk-planet abundance, are crucial to life as we know it, to mantle melting and volcanism, and to the climate (in-)stability of the Earth and beyond. Yet whilst every planet follows the same laws of chemistry, the specific roles of carbon and sulfur can play out to vastly different conclusions, as with Venus and the Earth. Clues to carbon and sulfur’s behaviour among the exoplanet population can be remotely accessed by observing their atmospheres. This session will explore the importance of these elements now and in deep time, across Earth, the Solar System, and exoplanets. We welcome new work from any discipline on carbon and/or sulfur in a range of contexts, from planet formation, mantle dynamics, and tectonics, to atmospheric chemistry and geobiology, progressing towards a cosmic picture of planetary evolution shaped by carbon and sulfur.