Catalytic reactions on metals are still nowadays involved in more than half of the chemical industrial processes. The winter school held at "I 'Ecole de in March 1996, 13 years after the first one, accounts Physique des Houches" for an evolution of the field in several directions. First, the emulation between theoretical chemistry and solid state physics has emerged on heuristic concepts, leading not only to explanations of the observed phenomena but, for the first time, to predictions of the reactivity of catalytic systems and of the reaction pathways. The second domain which during these years has become of primary importance is the abatement of the pollution. It concerns not only the conversion of polluting effluents but more and more major modifications of the processes to avoid the production of undesired products. Two striking examples are the necessary catalytic conversion of the 100 000 cubic meter of hydrogen that would be produced in a major incident of a nuclear power plant and the replacement of the CFC. The valorization of agricultural supplies can already be considered as one of the major achievement of catalysis. Indeed, the carbon of biosustainable raw materials represents more than 2 orders of magnitude the amount extracted from fossil fuels each year. Moreover, the molecules are already highly functionalised in contrast with hydrocarbons which require costly steps to be converted to the same products. They are now of current use in the elaboration of cosmetics, vitamins, polymers, etc.