The session revolves around the following themes, encompassing a whole range of scales in time and space, including water as agent in natural earthquake initiation, deep fracture fluids isolated in crust, activated degradation of organic matter in the deep biosphere, supercritical water for geothermal energy, metal-transporting hydrothermal fluids, sustainable energy and mineral resources, deep fluids and deep life, CO2 storage, and hydrofracking. Thus, the physics, chemistry and biology of subsurface fluids are all addressed.