Siderophores, biogenic chelating agents that facilitate Fe(III) uptake through the formation of strong complexes, also form strong complexes with Mn(III) and exhibit high reactivity with Mn (hydr)oxides, suggesting a pathway by which Mn may disrupt Fe uptake. In this review, we evaluate the major biogeochemical mechanisms by which Fe and Mn may interact through reactions with microbial siderophores: competition for a limited pool of siderophores, sorption of siderophores and metal-siderophore complexes to mineral surfaces, and competitive metal-siderophore complex formation through parallel mineral dissolution pathways. This rich interweaving of chemical processes gives rise to an intricate tapestry of interactions, particularly in respect to the biogeochemical cycling of Fe and Mn in marine ecosystems.