The other articles introduce frontier research topics in more typical land and marine environments, such as fluid flow in karst aquifers, the biological aspects of fluids in sedimentary basins and submarine sedimentary formations, respectively, and vigorous fluid flow in subsea formations and their significance in global tectonics. Geochemical characteristics of hydrothermal activities at a number of active continental margins are also reviewed, and multidisciplinary geophysical constraints of the permeability of young igneous oceanic crust are summarized. A variety of driving mechanisms for fluid flow is discussed in land and subsea formations; terrestrial hydraulic gradient, buoyancy driven free convection, tidally induced flow, flow induced by tectonic strain, flow due to sediment compaction.