The marine environment contains several habitats characterized by extreme living conditions. However, extremophilic marine fungi were neither well known, nor often studied. Many studies in recent years have shown that fungi do inhabit such habitats. Fungi are capable of withstanding high salinity conditions, such as those in intertidal mangrove environments and salt pans. Cold water, psychrotolerant fungi have been identified from polar waters. Numerous studies have shown that fungi grow actively in deep-sea sediments, under high hydrostatic conditions. Yeasts predominate deep-sea waters and many have also been shown to be psychrotolerant. Fungi have also been found in shallow water hydrothermal vents. Diversity studies on fungi in these habitats has shown the common presence of terrestrial species. Cryptic species and novel lineages have also been discovered . Extremophilic, or extremotolerant marine fungi could prove to be useful for biotechnological applications.