The production of H2 gas can be achieved at low temperatures using ruthenium‐based catalysts for the water–gas shift reaction (WGSR). Using a combined theoretical and experimental approach, D. M. Smith and co‐workers present in their Communication on page 741 ff. a new mechanism for the WGSR, involving anionic, Cl‐rich, Ru carbonyl complexes. The new understanding, which is supported by kinetic isotope effects, is a step towards large‐scale industrial production of H2 at low temperatures. [ABSTRACT FROM AUTHOR]