Iron–sulfur (Fe–S) clusters are ubiquitous prosthetic groups required to sustain fundamental life processes. The assembly of Fe–S clusters and insertion into polypeptides in vivo has recently become an area of intense research. Many of the genes involved are conserved in bacteria, fungi, animals and plants. Plant cells can carry out both photosynthesis and respiration – two processes that require significant amounts of Fe–S proteins. Recent findings now suggest that both plastids and mitochondria are capable of assembling Fe–S proteins using assembly machineries that differ in biochemical properties, genetic make-up and evolutionary origin.