Hydrothermal vents in deep and shallow ocean environments are geochemical conduits that link Earth’s interior with the oceans. These sites of active hydrothermal vents are distributed throughout the global network of ocean ridge spreading centers to ridge flanks and cool off-axis diffuse vent fields in ocean basins and occur in diverse lithological settings – including basalts, ultramafic rocks and sediments – and temperature regimes. These vents are loaded with nutrients from hydrothermal and magmatic activity that drive a vast sub-seafloor biosphere. Particularly near ocean ridge spreading centers magmatism and/or residual mantle heat serve as drivers for abiogenic mineral reactions generating reduced chemical species, which can be utilized by chemolithoautotrophic microbes. Additionally, microbial chemosynthesis within fluids drives near-vent productivity and support animal communities that inhabit these ecosystems. Water-rock-microbe interaction within the oceanic lithosphere considerably affects ocean water chemistry and the chemical composition of the oceanic lithosphere, effectively controlling global element cycles. This session seeks to combine new findings from a multi-disciplinary research community investigating the complex interplays between hydrothermal, magmatic and microbial processes in ocean floor settings, the diversity and extent of the shallow and deep subsurface biosphere, life in extreme environments, or their impact on global geochemical cycles. We also welcome contributions that study ongoing alteration processes and microbial activity in continental crust or oceanic lithosphere exposed on land, or ancient processes preserved in ophiolite sequences, from modern to Archaean systems.