Iron-sulphur (Fe-S) clusters have long been recognized as essential and versatile cofactors of proteins involved in catalysis, electron transport and sensing of ambient conditions. Despite the relative simplicity of Fe-S clusters in terms of structure and composition, their synthesis and assembly into apoproteins is a highly complex and coordinated process in living cells. Different biogenesis machineries in both bacteria and eukaryotes have been discovered that assist Fe-S-protein maturation according to uniform biosynthetic principles. The importance of Fe-S proteins for life is documented by an increasing number of diseases linked to these components and their biogenesis.