The reversible reduction protons to dihydrogen: 2H⁺ + 2e ⇌ H₂ is deceptively the simplest of reactions but one that requires multistep catalysis to proceed at practical rates. How the metal–sulfur clusters of the hydrogenases catalyse this interconversion is currently the subject of extensive structural, spectroscopic and mechanistic studies of the enzymes, of synthetic assemblies and of in silico models. This is driven both by curiosity and by the view that an understanding of the underlying chemistry may inform the design of new electrocatalytic systems for hydrogen production or uptake, pertinent to energy transduction technology in an ‘Hydrogen Economy’. Can chemists design materials that replace the expensive platinum metal catalysts of fuel cells with metal–sulfur cluster assemblies utilising abundant Ni, Fe and S as in the natural systems? Here we review the state of the art.