A new soil organic matter (SOM) model describing protection mechanisms and the potential saturation of soil organic carbon (SOC), in which the pools have been defined functionally, rather than kinetically, is presented. Over the past 20 years, simulation models of SOM have been used quite extensively to investigate the effects of tillage management, land use changes, changing climatic scenarios, and soil texture on SOM decomposition and storage. Recent research has suggested that models composed of functionally defined pools may better represent SOM dynamics as these pools are defined by physical and chemical fractionation schemes, rather than the unique decomposition kinetics (usually first-order) of each ‘pool.' The SATURN model is defined by both above- and below-ground pools, broken into three and eight pools, respectively. This model incorporates a new theory of potential SOC saturation and modern theories of soil aggregation and the physical and chemical protection provided therein, that were confirmed after steady-state analysis of the model.