Catalysts represent the oldest commercial application of nanotechnology. It is suggested that the focus of catalysis research in the 21st century should be on achieving 100% selectivity for the desired product (clean manufacturing). The molecular ingredients of selectivity are not well understood. The electronic and atomic structures of nanoclusters should be investigated as a function of their size, Because of the facile restructuring of metal clusters under reaction conditions they have to be characterized in situ. New synthetic methods need to be developed to produce catalyst particles with the same size, structure and location on the support.