This paper describes the state of the art of multiscale modeling of chemical solutions encountered in separation processes. It evidences the twofold role of modeling in the understanding and the prediction of selectivity of extracting molecules and gives an outline of the situation. First, the state of the art of the modeling techniques is given, and in the various sections the different levels of description, ranging from coordination mechanisms to macroscopic calculation of selectivity ratio, are presented. An overview of the main results is given, and a prospective roadmap to multiscale modeling is provided.