This book discusses the achievements in the study on the structure of active species being formed at the change of molecule charge or electronic state. It gives a systematic outline of the problem of molecular structure distortions in radical ionic and excited states involving experimental and theoretical material. The text focuses on analyzing the physical reasons for structural distortion occurrences at a model level and also with results of detailed quantum-chemical calculations. The book presents numerous facts on the structural distortions in ions of various types of organic molecules. Data is presented for the first time on distortions in radical ions of polyfluoroaromatics and other conjugated molecules.