This paper describes the electrochemical behavior of MoO2Cl2 at a platinum electrode in acetonitrile, methylene carbonate, and propylene carbonate solvents. Cyclic voltammetry, bulk electrolysis, and chemical reduction are used to show that on one-electron reduction of MoO2Cl2, MoO2Cl2- reacts with MoO2Cl2 to form an unusual Mo(VI)-Mo(V) dimer. This dimer can undergo both oxidation and further reduction. Oxidation to the Mo(VI)-Mo(VI) oxidation state is irreversible at low scan rates but reversible at high scan rates. Reduction of the dimer occurs in a reversible one-electron process to yield an Mo(V)-Mo(V) dimer which can be reduced further in a one-electron irreversible process. MoO2Cl2 partially ionizes in these solvents to give MoO22+, MoO2Cl42- and possibly MoO2Cl3- : and MoO2Cl42- are electrochemically active. Reduction of MoO22+ leads to electrodeposition of MoO2(s). An unusual irreversible oxidation wave is observed for MoO2Cl2, a d(0) species, which is due to oxidation of MoO2Cl42-. Solutions of MoO2Cl2 oxidize ferrocene : the solid obtained on drying was characterized by elemental analysis and IR spectroscopy.