We seek to convene a session that highlights the breadth of research on volatile elements in the deep Earth. Slabs subducted to the deep Earth carry with them volatile-rich, and perhaps oxidized, minerals that break down and transform as they encounter progressively higher pressures and temperatures. Fluids produced within slabs, along with volatiles trapped during accretion, are agents for mass transfer with a myriad of physical consequences, including weakened rheology, localized melting, and even diamond formation. Deep Earth volatiles are released to the atmosphere due to mantle advection and partial melting. The deep Earth also includes the core, and volatiles partition into core-forming metals, potentially causing large changes in density, seismic velocity, melting point, and convective power of the core. Taken together, the overwhelming mass of the deep mantle, and perhaps its volatile-rich nature, gives it leverage in determining the Earth’s volatile budget. We encourage submissions from all related disciplines.