The biosynthesis of the microbial small molecule iron scavengers known as siderophores has been of interest since their discovery in the middle of the past century. Two main pathways for siderophore biosynthesis exist. One is directed by a large family of modular multienzymes called non-ribosomal peptide synthetases (NRPSs) while the other is NRPS independent. There has been a vast increase in our knowledge of siderophore biosynthesis over the past two decades and the enzymology of several NRPS-dependent pathways is now well-understood while dramatic recent progress has also been made in elucidating NRPS-independent pathways. As siderophores are virulence factors in many pathogenic microorganisms, genetic and biochemical knowledge of siderophore biosynthetic pathways can aid in the development of new antimicrobials as well as increasing our understanding of the natural machinery for the efficient assembly of structurally complex bioactive natural products.