Surfactants such as SDS (sodium dodecylsulfate), membrane lipids, and proteins are amphipathic, containing both hydrophobic and hydrophilic domains. These groups of compounds are reviewed with reference to surfactant-phospholipid, surfactant-cell membrane, and surfactant-globular protein interactions. The binding of surfactants to proteins is examined from the standpoint of binding isotherms and the structures of the complexes determined by scattering techniques.