Iron is a vital element required by all microorganisms. In response to iron scarcity, both Gram-positive and Gram-negative bacteria synthesize siderophores—low molecular weight compounds with high iron-binding affinity—that serve as crucial virulence factors. Research has shown that impairments in the production or function of these molecules, as well as in overall iron acquisition systems, are associated with reduced bacterial pathogenicity. Given their involvement in diverse biological processes, siderophores have attracted considerable attention as important secondary metabolites. They also function as biosensors, monitoring iron levels in various environments. In the medical field, siderophores are exploited to deliver antibiotics into resistant bacteria via a Trojan horse strategy and are employed in the treatment of diseases such as cancer and malaria. This review examines iron acquisition mechanisms in both Gram-positive and Gram-negative bacteria, the significance of siderophore production in bacterial pathogenesis, the classification of siderophores, and their primary applications in medicine and industry.