Single-electron transfers to or from organic molecules result in the formation of anion-and cation-radicals, respectively. The removal of an electron from the bonding highest occupied molecular orbital (HOMO) or electron transfer to an antibonding lowest unoccupied molecular orbital (LUMO), respectively, leads to weakening of the corresponding bond. The bond becomes easier to break. The unpaired spin and charge can delocalize within the molecular carcass and this results in its attening. An unpaired electron can be localized on a functional group (atom), which leads to a change in the substituent effect. Appearance of an unpaired electron is accompanied with the emergence of an electric charge. The spin and charge can be delocalized together among the molecular constituents or spatially separated as in the distonic species. Each type has its own synthetic opportunities, which are discussed in the earlier chapters. This book as a whole shows that ion-radicals cannot be treated either as conventional radical particles or ionic species. They are characterized by a unique behavior. This is why this book uses the hyphen-bound term ion-radicals in contrast to the term radical ions, which is accepted in the Chemical Abstracts Classi cation Code.