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.