It is now recognised that extreme environments, once thought to be too hostile to permit survival of living organisms, are the natural habitat of certain microorganisms known as extremophiles. The discovery and characterisation of a wide array of microorganisms that thrive under extreme values of temperature, acidity, alkalinity, salt concentration and pressure led not only to major improvements in the understanding of the environmental conditions limiting life, but also in the descriptions of early stages of cellular evolution; Meanwhile the search results of adaptation mechanism and metabolites of extremophiles have markedly facilitated and improved our theory and technology in the biogeochemistry and biotechnological applications.