We describe in this paper the interaction between impurity and grain-boundary in solid solutions at the equilibrium. The different terms of the elastic interaction are first reviewed. One then calculates the electronic interaction of a heterovalent impurity with a boundary in a crystal of normal metal. One use pair interactions deduced from pseudo-potentials to calculate grain-boundary energies, the method being then extended to the calculation of the interaction with an impurity. This interaction is found oscillating and decreases with the distance as r-2. The resulting binding energy can be sizeable when compared with the elastic effect for highly misoriented boundaries