Approximately one-half of all proteins in cells require specific metal ions for proper function, which are delivered by specific auxiliary proteins called metallochaperones. Hydrogen producing enzymes, ［NiFe］ hydrogenases harbor a complex metal cofactor, NiFe（CN）2CO, in their active sites. Assembly and incorporation of the NiFe（CN）2CO center requires specific maturation machinery, in which six Hyp proteins （HypABCDEF） play key roles. Four Hyp proteins （HypC-HypF） are involved in the biosynthesis and incorporation of the Fe（CN）2CO group. After Fe insertion, HypA and HypB insert the Ni ion into the hydrogenase large subunit. Here, we review recent structural studies of Hyp protein complexes for ［NiFe］ hydrogenase maturation.