Volcanism manifests itself at the Earth's surface in various guises ranging from violent explosive injection of ash and gases into the atmosphere to sustained outpouring of lava onto vast land areas, or quiescent release of gas plumes that gently sweep the landscape downwind. By adding various amounts of carbon, sulfur and halogen gases, and silicate materials into the atmosphere and terrestrial and ocean environments, these volcanic phenomena have the potential to affect biogeochemical cycles over different spatial and temporal scales. While recognition of such interaction is not new, notably in relation to large ancient volcanic eruptions, quantitative data that can shed light on the interlinked mechanisms underpinning biogeochemical disturbances have only recently begun. This chapter provides an updated overview of the volcanic contributions to and effects upon the carbon, sulfur, and halogen biogeochemical cycles.