This book furthers readers understanding of the amazing features of six-membered transition states in stereoselective organic reactions. Comprehensive and logically organized, it covers reactions classified in four categories: [3,3]-sigmatropic rearrangements, aldol reactions, metal allylation reactions, and stereoselective reductions. There is a thorough discussion of each reaction category, along with computational studies that support a proposal of a six-membered state. The book assists professors, researchers, and students in proposing reasonable transition states for the description of newly discovered stereoselective reactions.