Hydrothermal systems in the continental and oceanic crust play fundamental role in the formation of mineral and hydrocarbon deposits, geothermal energy exploitation, and gas sequestration. Their dynamics relies on coupling across wide range of spatial scales, from pore-scale interactions to kilometer-scale flow patterns. These are currently addressed by a variety of observational, analytical, experimental, and modeling approaches. We encourage contributions addressing feedback relationships between crustal dynamics, fluid circulation, and rock reactivity as well as interpretations of their geological record.