Surface-active agents, or surfactants, owe their name to their interesting behavior at surfaces and interfaces. They are positively adsorbed at interfaces between phases, and the adsorption of surfactant lowers the interfacial tension between the phases (see Chapter 8). Because of their ability to lower interfacial tension, surfactants are used as emulsifiers, detergents, dispersing agents, foaming agents, wetting agents, penetrating agents, and so forth.