Understanding chemical reactivity has been the permanent concern of chemists from time immemorial. If we were able to understand it and express it quantitatively there would practically remain no unsolved mystery, and reactions would be fully predictable, with their products and rates and even side reactions. The beautiful developments of thermodynamics through the 19th century supplied us with the knowledge of the way a reactions progresses, and the statistical view initiated by Gibbs has progressively led to an unders­ tanding closer to the microscopic phenomena. But is was always evident to all that these advances still left our understanding of chemical reactivity far behind our empirical knowledge of the chemical reaction in its practically infinite variety. The advances of recent years in quantum chemistry and statistical mechanics, enhanced by the present availability of powerful and fast compu­ ters, are very fast changing this picture, and bringing us really close to a microscopic understanding of chemical equilibria, reaction rates, etc.... This is the reason why our Society encouraged a few years ago the initiative of Professor Savo Bratos who, with a group of French colleagues, prepared an impressive study on "Reactivite chimique en phase liquide", a prospective report which was jointly published by the Societe Fran