The extremely halophilic archaebacteria (halobacteria) became an early focus of scientific interest owing to their role in salted food deterioration. In more recent times their peculiar physiology involving extreme adaptation to the salt environment and other unique features have allowed the development of other applied interests. Their similarities to eukaryotic cells at the level of cell division justifies their use in the prescreening for anti-cancer drugs, and some of their antigens could be used for cancer diagnosis. Their unique retinal proteins can be used as light-biosensors and the use of the purple membrane (pm) as reversible holographic medium has already been developed. Halobacterial enzymes are an extremely tough raw material for enzyme technology, particularly for applications in which the reaction mixture has very low water activity. Thanks to their peculiar lipids and to the production of polysaccharides by some halobacteria, their cultures could be used for enhanced oil recovery. Some halobacteria are excellent producers of industrially interesting biopolymers. The use of halobacteria as producers of polyhydroxyalkanoates, biological polyesters such as poly-3-hydroxybutyrate, with the properties of biodegradable thermoplastics, is being considered.