Carbon dioxide (CO2) is the main compound identified as affecting the stability of the Earth's climate. A significant reduction in the volume of greenhouse gas emissions to the atmosphere is a key mechanism for mitigating climate change. Geological storage of CO2, or the injection and long-term stabilization of large volumes of CO2 in the subsurface in saline aquifers, in existing hydrocarbon reservoirs or in unmineable coal seams, is one of the more technologically advanced options available. A number of studies have been carried out and are reported here. They are aimed at understanding the safety, physical and chemical behaviour and long-term fate of CO2 when stored in geological formations. Until efficient, alternative energy options can be developed, geological storage of CO2, the subject of this volume, provides a mechanism to reduce carbon emissions significantly whilst continuing to meet the global demand for energy.