Scale-up and/or scale-down procedures are crucial during the development of chemical processes. These procedures should be integrated to form a multidisciplinary approach encompassing several branches of science and engineering. The challenge is to find a balance between chemistry, design, environment, hygiene and safety (EHS) compliance and economic factors. The iterative process of scale-up procedures also requires concept discrimination at early stages of process development. Scale-up studies should predict the reactor behavior and the quality and properties of a product from laboratory and pilot plant to full scale; however, not every pilot scale presents a valid industrial scaled-down size. A rational mathematical model describing the process reasonably well for large scale is important for designing industrial processing units, but this is only feasible if a phenomenological understanding is achieved, and if the necessary constants and parameters are estimated accurately. An accomplished process development procedure must lead to products presenting the same properties at both small and large scale.