It is now more than 20 years since the book "Radical Ions" edited by
Kaiser and Kevan appeared. It contained aspects regarding generation,
identification, spin density determination and reactivity of charged
molecules with an odd number of electrons. New classes of reactive ion
radicals have been detected and characterised since then, most notably
cation radicals of saturated organic compounds. Trapping of electrons
has been found to occur not only in frozen glasses but also in organic
crystals. The structure and reactions of anion radicals of saturated
compounds have been clarified during the last 20 years. We have asked
leading experts in the field to write separate chapters about cation
radicals, anion radicals and trapped electrons as well as more complex
systems of biological or technological interest. More attention is paid
to recent studies of the ions of saturated compounds than to the older
and previously reviewed work on aromatic ions. In the case of trapped
electrons full coverage is out of the question, and focus is on recent
efforts to characterise the solvation structure in ordered and
disordered systems.