The biogeochemical cycling of sulfur between the lithosphere, atmosphere, hydrosphere, and biosphere has played a pivotal role in the emergence and evolution of life and in the changing oxidation state of the Earth’s surface over the last 4 billion years. As a macronutrient, sulfur is essential for the formation of proteins, electron transport chains, and various critical biomolecules present in cells across all domains of life. A wide variety of microorganisms support their metabolism through energy released by redox transformations of sulfur. These metabolic processes link the carbon and sulfur cycles and affect the oxidation state of Earth’s surface. The resulting biogeochemical feedbacks result in isotope partitioning, creating differences in stable isotope ratios of oxidized and reduced forms of sulfur, and these differences are incorporated into sulfur-bearing minerals. The isotope ratios in these minerals serve as tracers of the past sulfur cycle, though their preservation is imperfect and is affected by a range of environmental processes.