This book emphasises those features in solution chemistry which are difficult to measure, but essential for the understanding of both the qualitative and the quantitative aspects. Attention is paid to the mutual influences between solute and solvent, even at extremely small concentrations of the former. The described extension of the molecular concept leads to a broad view — not by a change in paradigm — but by finding the rules for the organizations both at the molecular and the supermolecular level of liquid and solid solutions.