Maturation of [FeFe]-hydrogenases, consisting in the synthesis and assembly of a di-iron center with a dithiolate bridging ligand as well as CO and CN ligands, depends on the concerted action of three metalloproteins, HydE, HydF and HydG. HydE and HydG are "Radical-SAM" enzymes involved in the synthesis of the ligands. HydF is proposed to function as a scaffold protein in which the di-iron center is assembled before being transferred to the hydrogenase. Here we review the current knowledge regarding the structure of the three maturases and the mechanisms of synthesis and assembly of the di-iron center of [FeFe]-hydrogenases. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.