A survey of the global carbon reservoirs suggests that the most stable, long-term storage mechanism for atmospheric CO2 is the formation of carbonate minerals such as calcite, dolomite and magnesite. The feasibility is demonstrated by the proportion of terrestrial carbon bound in these minerals: at least 40,000 times more carbon is present in carbonate rocks than in the atmosphere. Atmospheric carbon can be transformed into carbonate minerals either ex situ, as part of an industrial process, or in situ, by injection into geological formations where the elements required for carbonate-mineral formation are present. Many challenges in mineral carbonation remain to be resolved. They include overcoming the slow kinetics of mineral-fluid reactions, dealing with the large volume of source material required and reducing the energy needed to hasten the carbonation process. To address these challenges, several pilot studies have been launched, including the CarbFix program in Iceland. The aim of CarbFix is to inject CO2 into permeable basaltic rocks in an attempt to form carbonate minerals directly through a coupled dissolution-precipitation process.