The enzymatic promiscuity concept involves the possibility that one active site of an enzyme can catalyse several different chemical transformations. A rational understanding of the mechanistic reasons for this catalytic performance could lead to new practical applications. The capability of certain hydrolases to perform the perhydrolysis was described more than a decade ago, and recently its molecular basis has been elucidated. Remarkably, a similarity between perhydrolases (cofactor-free haloperoxidases) and serine hydrolases was found, with both groups of enzymes sharing a common catalytic triad, which suggests an evolution from a common ancestor. On the other hand, several biotechnological applications derived from the capability of hydrolases to catalyse the synthesis of peracids have been reported: the use of hydrolases as bleaching agents via in situ generation of peracids; (self)-epoxidation of unsaturated fatty acids, olefins, or plant oils, via Prileshajev epoxidation; Baeyer-Villiger reactions. In the present review, the molecular basis for this promiscuous hydrolase capability, as well as identified applications are reviewed and described in detail.