Publisher Summary This chapter discusses the role of chemical reaction engineering in sustainable process development. It is reviewed how some micro-level concepts such as atom efficiency and optimum catalyst development affect reactor choice and pollutants generated. At the meso-level, optimizing the catalyst properties and choosing the right media significantly reduces the adverse environmental impact of chemical processes. Clearly, proper understanding and application of the principles of multiphase reaction engineering are very important for proper execution of truly environmentally benign processes since almost all processes involve more than one phase. At the macro-level, it is crucial to estimate the hydrodynamic effects on reactor performance as this will lead to the selection of the right reactor. Furthermore, novel approaches to reactor design using process intensification concepts can be implemented to improve efficiency and minimize pollution. In addition, environmental impact analysis of the developed process has to be evaluated to see if green chemistry conditions are met and to assess the overall global impact of these changes.