This extraordinary textbook presents tools, methods and models for the understanding organic reactions. It helps to answer questions like "Why is a reaction possible?" or "What reaction products can I expect?". The first chapters about chemical equilibria, thermodynamics, reaction rates and the MO theory are giving the reader a solid background in physical organic chemistry. The following chapters illustrate a large number of reactions involving organic, organometallic, and biochemically important reactants and catalysts with a wide practical value in synthesis and biology, e.g. pericyclic reactions, photochemical reactions, catalytic reactions and C-C-bond forming reactions. Here, the reader finds tools to plan efficiently a chemical reaction, to control and create new chemistry. Written by two international highly renowned experts, this textbook is not only a resource for graduate students, PhD student and postdocs, but also for chemists and chemical engineers who develop new reactions and procedures. In addition, each chapter contains numerous questions and answers which are available online.