The need to stabilize atmospheric carbon dioxide levels may lead to requirements for reduction of carbon dioxide emissions from coal and other fossil fuel-fired power plants. Carbon dioxide capture and storage (CCS), involving capture of the CO2 at the plant, compression, transport, and injection into the deep subsurface, is a technology which is available in the near-term. The primary targets for geologic storage are sedimentary basins containing porous, saline water-saturated formations, oil and gas reservoirs, and deep, unmineable coals. Since, under most conditions in the subsurface, CO2 will be buoyant relative to the formation fluids, possible leakage from the injection intervals is a primary risk of geologic storage. The buoyancy of CO2 is counteracted, however, by naturally occurring low permeability seals, structural traps, and other chemical and physical processes, so the risk of leakage can be mitigated by a combination of careful site characterization, controlled injection, and monitoring. Much of the technology needed for carrying out these activities has already been developed in support of the exploration and production of oil and gas, natural gas storage projects, acid gas disposal, and the use of CO2 to enhance oil production. Regional assessments and field pilot tests are still needed, however, in order to provide critical knowledge and experience needed for large-scale deployment of geologic storage. Capture remains the largest cost component of geologic storage, motivating additional research to develop new approaches. The impact on rock-water interactions of the composition of the gas stream resulting from new developments will need to be addressed.