Reaction engineering in fine chemicals manufacture is an integral part of the process development and design. It requires a multidisciplinary collaboration to implement complex organic chemistry within tight time and cost pressures. The commercial viability of a chemical route can be determined by the ability to handle complex mixtures and to obtain maximum selectivity and yield in multi-phase reaction mixtures where reaction rates, mass transfer rates and dispersion and coalescence rates all interact. Whilst much of the equipment used may appear superficially to be rather simple, in practice, where development is carried out at a world-leading level, the underlying principles and understanding of the dynamics of the competing rate processes and the fundamental mechanisms can be very complex. Examples of reactor selection and design on cost and safety grounds are described and the techniques used to address problems of competing reaction and mass transfer, dispersion and coalescence and competing fast reactions are illustrated. A number of opportunities for improved reactor design are discussed to meet ever more demanding capital and operating cost constraints and chemical efficiency requirements, driven by the desire to reduce the impact of the manufacture and use of fine chemicals on the environment and by increasing competition.