Surfactants are the surface-active molecules that display amphiphilicity, Because of this surface activity and amphiphilicity, surfactants have been used in wide industrial applications such as foods, detergents, cosmetics, medicine, polymers, paints, flotation, textiles. These days, their applications extend to high-technology industries such as microelectronics, magnetic recording material, advanced batteries, novel separations, etc. As new applications of surfactants are found and the demand of the surfactants increases, surfactant industry has been more pressed to face a formidable challenge, which is to develop surfactants that are envirionmentally friendly. In this regard biosurfactants may be alternatives to chemical surfactants, since biosurfactants are biologically compatible, more biodegradable, less toxic, and highly specific. Because of these excellent advantages over those of chemical surfactants, much efforts have been made in biosurfactant research. This article reviews biosurfactants in several aspects, that is, their definition, structures, properties, applications, and prospects.