The reuse of agro-industrial wastes in solid-state fermentation (SSF) processes is of particular interest due to their availability and low cost, besides being an environment friendly alternative for their disposal. This chapter deals with the use of agro-industrial wastes in SSF processes. Initially, an overview about the generation of these wastes and their chemical composition is presented. In the sequence, the characteristics of SSF systems and variables that affect the product formation by this process are reviewed and discussed. Finally, potential applications of agro-industrial wastes in SSF processes for obtaining value-added compounds are described.