Early in the debate on global warming and greenhouse gas emissions, agricultural soils were identified as a potential depository of atmospheric carbon dioxide (CO2), and terrestrial carbon (C) sequestration was identified as a means of mitigating greenhouse gas emissions. The progression of research pertaining to terrestrial C sequestration has moved from the estimation of the technical potential of soils to store CO2 to an examination of the economic and policy aspects of soil C sequestration.