Creating a drug is a complex process involving many departments and different jobs, and chemists play an important role in both drug discovery and development phases. The goal of process chemistry, traditionally, has been to develop scalable synthetic routes that are safe, cost-effective, and environmentally benign. In modern pharmaceutical research, however, with increasing demand for accelerated drug discovery and early establishment of viable manufacturing route, the process chemistry’s role has expanded to encompass from enabling drug discovery to regulatory filing support. The increased responsibility, in turn, presented a range of different challenges that require strategies appropriate to each development phase. In this presentation, a series of chemistry development examples will be discussed to illustrate how process chemists at MSD address challenges in different stages of drug development.