The understanding of chemical reactivity is of key importance for the development and optimization of key chemical processes in both the laboratory and industry. Solvation not only changes the properties of the reactants and the products, but also affects transition states. Solvents thus influence the thermodynamics, the kinetics, and the product selectivity in liquid phase reactions. The selection of a suitable solvent frequently determines the success or failure of a chemical reaction. One example with possibly broad implications is the synthesis of enantiomeric pure products that is mandatory for any new drug development. This poses the scientific challenge of developing highly stereoselective synthetic strategies, for which the choice of a suitable solvent system is crucial. Furthermore,alternative sustainable technologies – ”green chemistry” – require novel designer solvents, which reduce or eliminate the use of hazardous substances in the production and application of chemical products. A new stage in technological sorption and purification processes has been entered with the development of ionic liquids as green solvents. Nonconventional solvent mixtures are just being explored for the more effective conversion of biomass to feedstock chemicals. Focusing on strategies for the design and use of nonconventional solvents in chemical reactions will undoubtedly help to improve the efficiency in many important chemical process technologies. The new insights will have a significant impact by removing some of the crucial barriers to the development of new, sustainable technologies, including “green chemistry“.