Carbon dioxide capture and storage (CCS) in deep geological formations has recently emerged as an important option for reducing atmospheric greenhouse gas. CO2 injected into deep underground is considered to be dissolved in formation water filling the reservoir formation and to reduce water pH by dissociation. The acidified water is expected to react with minerals forming the reservoir rocks to promote their dissolution and alteration toward a final goal of the precipitation of new phases that are stable in the presence of a large amount of CO2. A series of rock-water interaction summarized above is called “geochemical CO2 trapping” that is expected to stabilize CO2 geological storage system in a long period. This and the next issues of the Japanese Magazine of Mineralogical and Petrological Sciences collect papers concerning to the rock-water interaction associated with CO2 geological storage. The storage options as a background of individual study are largely similar to those reviewed in IPCC (2005), however, a unique option matching with geology of the Japanese Islands as a young volcanic arc is also included.