Proteases catalyze the hydrolysis of peptide bonds in proteins/peptides inside or outside of cells. They play important roles in development and responses to environmental stresses. In arbuscular mycorrhiza (AM), symbiosis-induced protease genes were found by large-scale transcriptome analyses in different plant species, suggesting that proteolytic processes are implicated in AM. In legumes, some of these were also transcriptionally activated during the root nodule symbiosis. However, the precise function of these symbiosis-induced proteases remains unknown. Here we present a compilation of the symbiosis-induced proteases identified so far and discuss their possible roles in symbiosis.