Advances in molecular biology and the many -omics fields promises to continually deliver new targets for drug development. Bringing these breakthroughs to the general public as useful drugs, however, entails an intricate path. This is particularly true for vaccine and therapeutic products which, unlike small drug molecules, can involve complex systems and very large biomolecules. Bioprocessing plays a key role along the path of developing these products by providing high-quality candidates for safety assessment, preclinical and formulation studies and for the clinical trials as well as developing production processes scalable for manufacturing of a licensed product. Analytical capabilities such as mass spectrometry must be at hand to ensure a well characterized and consistent product. Here, examples will be shown highlighting some of the key contributions made by mass spectrometry in the development and bioprocessing of Merck vaccines and therapeutic protein products.