The end of the previous millennium saw an explosion in the application of parallel synthesis techniques for making compounds for high-throughput screening. Over time, it became clear that more thought in the design phase of library development is necessary to generate high quality hits. More recently, the use of parallel synthesis techniques has shifted to applications beyond screening collections. Exploring the nuances of this technology, High-Throughput Lead Optimization in Drug Discovery describes the application of parallel synthesis to lead optimization and the design and synthesis of targeted libraries.