The colonization of cultural heritage by microorganisms is a planetary problem occurring in all countries, under any climate and on any type of object. Microbial aggression results in aesthetic and structural damage. Depending on chemical composition and ambient conditions, different groups of microorganisms adhere to and grow onto cultural artefacts. Whereas there is a general consensus that microorganisms play a role in the degradation of cultural heritage, much remains to be done for the identification of the specific microorganisms responsible for the damage, the mechanism of their action and the interrelations between the different microbial species that may be present on cultural heritage.