Hydrogenases catalyze the reversible oxidation of H , which is crucial for the anaerobic metabolism of microorganisms. They attract growing interest in connection with H -based energy systems. [NiFe] hydrogenase is the most common type among the currently known hydrogenases, and its active site consists of an "organometallic" Fe-Ni complex supported by cysteinyl thiolate ligands. This review presents an overview of the synthesis, properties, and reactions of thiolate-bridged iron-nickel complexes that model the active site of [NiFe] hydrogenase. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA. 2 2