The GEFSOC Soil Carbon Modeling System was assembled under a co-financed project supported by the United Nations Environment Programme (UNEP) Global Environmental Facility (GEF) and the U.S. Agency for International Development. The tool was built to provide scientists, natural resource managers, policy analysts, and others with the tools necessary to conduct regional- and country-scale soil carbon inventories. It is intended to allow users to assess the affects of land use change on soil carbon stocks, soil fertility, and the potential for soil carbon sequestration. The tool was developed in conjuction with case-study land use and soil carbon analyses conducted by scientists living in four countries: Brazil, Jordan, Kenya, and India. The analyses were conducted on the Brazilian Amazonian region, the entire countries of Jordan and Kenya, and the Indo-Gangetic plain of India. As such it has been tested as a proof of concept in developing tropical countries with diverse land use patterns and pressing problems with agricultural soils fertility. The tool requires a minimum of two off-the-shelf computers with basic networking capabilities, one running Microsoft Windows® and one or more running Redhat® LINUX, connected via a networking switch. It utilizes to the maximum extent possible open-source software that is freely available for downloading off the web. The tool conducts analysis using three well-recognized models and methods, including: 1) the Century general ecosystem model; 2) the RothC soil carbon decomposition model; and 3) the Intergovernmental Panel on Climate Change (IPCC) method for assessing soil Carbon at regional scales. The tool interacts with a SOTER database developed for the country or region the user intends to model. A demonstration of the tool and results from assessing land use change in the four case-study countries will be presented.