AbstractDecomposition is the sum of a large number of species interactions that occur in the soil food web. These can be simplified into a set of interactions among functional groups. This chapter discusses the global impact of decomposition. The fate of nutrients in the litter, through saprotrophs and into the soil solution is also analysed. Soil food web models are constructed based on the estimates of nutrient flux through various compartments. The models are then used to determine stability or dynamic behaviour of the food web under simulated manipulations.