Discharge and charge reactions of MoO 3 electrodes in organic Li + electrolytes are shown to be reversible topotactic redox processes of layered molybdenum bronzes Li x+[MoO 3] x- . The kinetically accessible charge range amounts to 0.1 ⪕ x < 1.5 with the lower limit of x depending on the precedent cathodic load. Complete re-oxidation to the binary oxide is kinetically hindered presumably as a result of small structural changes. The process is strongly affected by the size of the electrolyte cation, whereas no dependence on the anion species was observed. Reduction beyond x = 1.5 is at least partially associated with irreversible changes in the oxide structure. Similar reactions were found for non-stoichiometric molybdenum oxides e.g. Mo 18M 52 and Mo 8O 23.