Professor Eli Ruckenstein was a pioneer in numerous areas of nanosciences. In catalysis, he was the first to bring scientific principles and quantitative reasoning to bear on the aging and rejuvenation of supported metal catalysts; he developed a quantum chemical theory of poisoning and promotion of metal catalysts and proposed a pumping mechanism for the catalytic oxidation by mixed oxides. He developed methods to prepare hydrophobic and hydrophilic nano-reservoirs containing active but dangerous catalysts and used them to prepare interesting compounds; he controlled the selectivity of some reactions via hydrophilic recognition by polymer-supported catalysts. He initiated the modern thermodynamics of microemulsions and developed the first predictive theory of micellization and solubilization. He explained the restabilization of colloids at high ionic strengths. He provided explanations for the enhancement of enzymatic reactions in inverted micelles and developed theories for hydration forces, hydrophobic attraction, and the thermodynamic stability of dispersions (lamellar liquid crystals, phospholipid monolayers, phospholipid bilayers, and microemulsions). He developed a theory for the sticking probability of aerosols, theories regarding specific ion effects on surface tension and double layers, and a kinetic theory of nucleation free of macroscopic concepts. Ruckenstein has developed new technologies in catalysis and in the preparation of complex materials that possess enhanced properties, such as pastes with high thermal conductivity, membranes for separation processes, and tough polymeric materials.