Siderophore-drug conjugates are three component systems consisting of a siderophore, linker, and drug (Fig. 2; Fig. 3). All three components serve an important function. The role of the siderophore is well understood (see earlier discussion), but less attention has been given to the nature of the drug and the stability of the linker. The drug (structure activity relationships and target location) determines if drug release is necessary for activity while the linker determines if this release is possible in cells.