The volatile constituents—H2O, CO2, and S, and Cl—play an important role in the generation, evolution, and eruption of magma. Knowledge of the abundance and flux of these volatiles is important for understanding the hazard implications of volcanic activity, explosive eruptive behavior of volcanoes, recycling of volatiles in subduction zones, formation of magmatic-hydrothermal ore deposits, additions of volcanic gases to Earth's atmosphere, and potential climatic impacts of large volcanic eruptions.

Over the past 25 years, new developments in technology have led to major advances in our ability to measure the fluxes of volatiles released from erupting volcanoes. At the same time, new micro-analytical techniques have made it possible to measure the pre-emptive concentrations of magmatic volatiles through the use of tiny melt inclusions trapped in phenocrysts in volcanic rocks. Comparison of the data acquired from these different perspectives has highlighted some major gaps in our understanding of both the abundance of the different volatiles, and the ways in which they are transported through magmatic systems and released to the atmosphere by degassing.