Book excerpt: Written with the practicing medicinal chemist in mind, this is the first modern handbook to systematically address the topic of bioisosterism. As such, it provides a ready reference on the principles and methods of bioisosteric replacement as a key tool in preclinical drug development. The first part provides an overview of bioisosterism, classical bioisosteres and typical molecular interactions that need to be considered, while the second part describes a number of molecular databases as sources of bioisosteric identification and rationalization. The third part covers the four key methodologies for bioisostere identification and replacement: physicochemical properties, topology, shape, and overlays of protein-ligand crystal structures. In the final part, several real-world examples of bioisosterism in drug discovery projects are discussed. With its detailed descriptions of databases, methods and real-life case studies, this is tailor-made for busy industrial researchers with little time for reading, while remaining easily accessible to novice drug developers due to its systematic structure and introductory section.