Hypersaline environment is an extreme habitat dominated by high salt concentration. Associated to this extreme condition, other extreme conditions can be found like low oxygen concentration and alkaline conditions. The inhabitants of these environments are microorganisms that are called “halophiles.” Halophiles have to solve the problem of the osmotic pressure generated in the cell membrane. To do that, they can use compatible solutes. Different groups can be distinguished on the basis of their physiological responses to salt. Several classifications have been proposed; one considers the optimum growth of the microorganisms at different salt concentrations: non-halophiles are those that grow best in media containing less than 0.2 M NaCl, halotolerant microorganisms that can tolerate high salt concentrations, moderate halophiles growing between 0.2 and 2.5 M NaCl, and extreme halophiles growing in optimal conditions at high salt concentration (2.5–5.2 M NaCl).