Due to their delocalized electronic structure, 1,2-dithiolene complexes undergo reversible redox reaction. When oxidized, dithiolene complexes have greater 1,2-dithioketone character. In reduced complexes, the ligand assumes more ene-1,2-dithiolate character. These descriptions are evaluated by examination of differences in C-C and C-S bond distances. The true structure lies somewhere between these resonance structures. Reflecting the impossibility to provide an unequivocal description of the structure, McCleverty introduced the term 'dithiolene' to give a general name for the ligand that does not specify a particular oxidation state. This suggestion was generally accepted, and 'dithiolene' is now a universally accepted term. Only more recently the radical nature of monoanionic 1,2-dithiolene ligands has been pointed out. While few examples of authentic dithiolene radicals have been reported, diamagnetism in neutral bis(1,2-dithiolene) complexes of divalent transition metal ions should be considered as a consequence of a string antiferromagnetic coupling between the two radical ligands.