Despite the importance of soil C reservoirs, global estimates of soil C stocks to different depths (0.5, 1, 2 or 3 m) are highly variable, obtained by diverse and non-standard procedures and are not available at all for several key ecosystems. Soil C stocks, which vary over time and space and with land use and management, are temperature sensitive and vulnerable to climate change. Global hotspot ecosystems must be protected, restored, managed and, in some cases in which land is marginal for agriculture, returned to nature in order to mitigate climate change, improve water quality and strengthen biodiversity. Technologies for restoring soil organic carbon stocks include landscape management, conservation agriculture based on residue mulch with cover cropping and complex rotations, agroforestry, integrated nutrient management, improved grazing and pasture management, reclamation of saline soils and the restoration of degraded soils. Urban soils are a large sink for C and these ecosystems must be designed and managed judiciously.