Publisher Summary Intelligent engineering can drastically improve process selectivity as illustrated in this chapter. The chapter discusses the selectivity engineering in the heterogenization of homogeneous catalysis. Catalysts play a very important role in processes with integrated environmental protection. Both heterogeneous and homogeneous catalysts are important. Catalyst engineering and process engineering are important in realizing high selectivity and productivity for the reaction. The manufacture of fine chemicals, which cater for a very wide variety of industries such as pharmaceuticals, agrochemicals, fragrances and flavors, dyestuffs, photography and textiles, depends heavily on catalysts and process engineering. Heterogeneous catalysts offer higher selectivity than homogeneous catalysts. The selectivity of ion-exchange catalysts often leads to yields that are considerably higher than those obtained with catalysis by dissolved electrolytes. The use of a two-phase system allows a change in the selectivity. The activity and selectivity can be manipulated through matching of polarity between the catalyst and the biphasic system. Higher selectivity, easier processing, use of inexpensive solvents, use of cheaper chemicals, and ease of heat removal have been realized through phase-transfer catalysis.. Micelles are aggregates of surfactants and are capable of dissolving large quantities of hydrophobic substances; ionic reagents are also taken up due to electro-static interactions. The ability of micelles, by manipulation of charge to repel ionic species, can be exploited to inhibit undesired reactions and thereby improve selectivity.