The different methods available in the literature to calculate the surface tension of a solid from contact angle measurements are discussed and compared. The discussion is based on the contact angles of water, glycerol, and diiodomethane measured at 20 degrees C on the surface of a side-chain liquid crystalline polymer, Some discrepancies exist among the results obtained with the different methods, mainly between the values yielded by Neumann’s equation and those obtained with approaches that postulate the decomposition of the surface tension into several terms associated with different types of molecular interactions (methods of Owens and Wendt and of Good and van Oss). The physicochemical basis of these various treatments is discussed.