The practice of regulatory science (RS) for drug development is described. In the course material for education in pharmaceutical sciences drafted by the RS Division of the Pharmaceutical Society of Japan, RS for pharmaceuticals is defined as the science of predicting, assessing, and judging the quality, efficacy, and safety of pharmaceutical products throughout their lifespan. RS is also described as an integrated science based on basic and applied biomedical sciences, including analytical chemistry, biochemistry, pharmacology, toxicology, genetics, biostatistics, epidemiology, and clinical trial methodology, and social sciences such as decision science, risk assessment, and communication science. The involvement of RS in drug development generally starts after the optimization of lead compounds. RS plays important roles governing pharmaceuticals during their entire life cycle management phase as well as the drug development phase.