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Much of the Antarctic continent's microbiota is restricted to endolithic: microecosystems which harbour distinct microbial communities as biofilms. The lithic substrate and the microorganisms comprising these films are intimately linked, giving rise to complex mineral-microbe interactions. The Antarctic biofilms; analysed in this study were characterised by the presence of extracellular polymer substances. Cyanobacteria appeared as key components of these biofilms in zones where there were no nearby lichen thalli. Fungal cells were the predominant organisms in areas inhabited by epilithic lichens. The combined use of microscopy and molecular techniques enabled the identification of the different biological components of biofilms found in subsurface layers of the lithic substrate. It is proposed that in this extreme environment, the structure of the biofilm may favour the formation of microsites with specific physicochemical conditions that permit the survival of microbial communities.