Hydration of mantle rocks, whether occurring at the seafloor or in the mantle wedge, results from/in strongly interconnected thermal, mechanical, mineralogical, and chemical processes, and contributes significantly to mass budgets of key chemical compounds (e.g. C, S, Fe, Cl…) from ocean ridges to subduction zones and back into the mantle. It can also sustain ecosystems whose primary energy sources are chemosynthetic. In this session, we encourage contributions ranging from field study (ophiolitic complexes, dredges or drilled samples and hydrothermal fields, among other settings), thermodynamic and numerical modeling to experimental work on serpentinization processes at mid-ocean ridges and in subduction zones. We also seek contributions on observational, theoretical and/or experimental studies on companion processes, in particular those related to C cycle such as carbonation of ultramafic rocks and their potential for CO2 sequestration in nature.