Description of equilibrium grain boundary segregation in multicomponent systems based on the Guttmann's approach is briefly introduced and the effects of individual variables (temperature, type and chemical composition of the system, type and structure of the interface) on the level of segregation are discussed. A method is outlined which enables predicting the enthalpy of segregation of individual solutes at individual grain boundaries in a chosen matrix on the basis of the solid solubility data (grain boundary segregation diagrams). The relationship between segregation enthalpy and entropy is suggested. The change of the cohesion energy induced by the grain boundary segregation can serve for example of its influence on other properties of the material.