The biocorrosion and biodeterioration of limestone and sandstone by epilithic and endolithic lichens was studied using the maceration and the casting-embedding techniques. The investigations revealed alterations on the rock surface, characterized by biocorrosive pitting, etching patterns, imprints of the fruiting bodies, boring channels and mucilaginous etching figures. Moreover, the inside of the rock is penetrated by extensive and compact networks of the lichenized fungal hyphae. These biodeteriorations are positively correlated to the physical and chemical actions of the lichen involved as well as to the nature of the rock.