The overall effects of fire on ecosystems are complex, ranging from the reduction or elimination of aboveground biomass to impacts on belowground physical, chemical and microbial mediated processes. Since a key component of overall ecosystem sustainability occurs belowground, recovery is tied to the soil's physical, chemical, and biological functions and processes. Depending on several fire severity measures, changes in belowground components can be either beneficial or deleterious to the entire ecosystem. Low-impact burning can promote a herbaceous flora, increase plant available nutrients, and thin over- crowded forests, all of which can foster healthy systems. Severe fires can often cause changes in successional rates, alter above- and belowground species composition, generate volatilization of nutrients and ash entrainment in smoke columns, produce rapid or decreased mineralization rates, alter C:N ratios, and result in subsequent nutrient losses through accelerated erosion, leaching or denitrification. In addition, changes in soil hydrologic functioning, degradation of soil physical properties, decreases in micro- and macrofauna, and alterations in microbial populations and associated processes can occur. The direct effect of fire on belowground systems is a result of the burning severity, which integrates aboveground fuel loading (live and dead), soil moisture and subsequent soil temperatures, and duration of the burn. The time for recovery of belowground systems will not only depend on the burning intensity and its effect on key ecosystem processes and components, but also on the previous land-use practices. Thus, the impacts of fire on belowground systems can be highly variable and may not be predictable. Our paper is a general review of the effects of fire on belowground systems with emphasis placed on the changes in physical, biogeochemical and biological properties of soils and the resulting consequences these changes have for ecosystem sustainability.