The long-awaited successor to the classic textbook "Boundary Orbitals and Reactions of Organic Compounds." This completely revised and updated edition includes molecular orbital theory and numerous other topics. Using molecular orbital theory, the distribution of electrons in molecules can be described. This allows for predictions about the spatial structure, physical properties, and reactivity of chemical compounds. The molecular orbital theory is explained here in an easily understandable manner, avoiding complex mathematical treatment, and is supported by many illustrative examples. This book is essential reading for all advanced undergraduate students, master's students, and doctoral candidates.