Pharmaceutical manufacturers are facing ever-growing needs of quality by design practices for the development of robust and predictable chemical processes. In this context, the use of modern simulation techniques has emerged as a valuable tool to cope with these demands. To illustrate the potential of this approach we will cover some of the challenges faced during process development and scale-up regarding sensitive crystallizations, gas-liquid reactions, liquid-liquid extractions and equipment design emphasizing on the mixing phenomena. The use of mixing simulation tools increases the understanding on the chemical processes during Active Pharmaceutical Ingredient (API) manufacturing. This allows chemists and process engineers to mitigate risk, achieve better performances and long lasting results.