Soil carbon (C) is a dynamic and integral part of the global C cycle. It has been a source of atmospheric carbon dioxide (CO₂) since the dawn of settled agriculture, depleting more than 320 billion metric tons (Pg) from the terrestrial pool, 78±12 Pg of which comes from soil. In comparison, approximately 292 Pg C have been emitted through fossil-fuel combustion since about 1750. However, terrestrial pools can act as a sink for as much as 50 parts per million of atmospheric CO₂ for 100 to 150 years. The technical sink capacity of US soils is 0.288 Pg C per year; Earth's terrestrial biosphere can act as a sink for up to 3.8 Pg C per year. The economic potential of C storage depends on its costs and cobenefits, such as global food security, water quality, and soil biodiversity. Therefore, optimally managing the soil C pool must be the bash of any strategy to improve and sustain agronomic production, especially in developing countries.