X-ray crystallography remains the most robust method to determine protein structure at the atomic level. We demonstrate how these structural studies can directly contribute to unsolved problems in biology, with a focus on the growing problem of antibiotic resistance in bacterial infections. Multi-drug efflux transporters are common and powerful resistance mechanisms that are capable of extruding a number of structurally unrelated antimicrobials, including antibiotics and toxic heavy metal ions, from the bacterial cell. We begin by presenting the crystal structures of the individual pump components of the Escherichia coli Cus system, a paradigm for efflux machinery, and speculate on how these pumps assemble to fight diverse antimicrobials. In Mycobacterium tuberculosis, the cell wall is critical to the virulence and antimicrobial resistance of these pathogens. Recent work shows that the MmpL transporter family contributes to cell wall biosynthesis by exporting fatty acids and lipidic elements of the cell wall. The expression of the M. tuberculosis MmpL proteins is controlled by a complex regulatory network, including the TetR family transcriptional regulators Rv3249c and Rv1816. We demonstrate how the structures of these two proteins enhance understanding of the MmpL family of proteins and to develop new antibacterial tools to fight tuberculosis. Neisseria gonorrhoeae is a Gram-negative human pathogen and the cause of the STD gonorrhea. In N. gonorrhoeae, the MtrCDE multidrug efflux system mediates resistance to diverse antibiotics, nonionic detergents, antibacterial peptides, bile salts, and steroidal hormones. We have developed several techniques to assemble the complete MtrCDE tripartite efflux complex, which we present here. These efforts have culminated in a low-resolution structure of the bipartite MtrCD complex. Finally, we apply our crystallography techniques to the problem of chloroplast cell division. In plants and algae, chloroplast division proceeds by binary fission, involving the coordinated assembly of four rings, both inside and outside the cell. We have determined the first high-resolution crystal structure of the Arabidopsis thaliana cell division protein PARC6. In addition, we obtained the co-crystal structure of PARC6 and PDV1, another protein within this network, revealing the molecular details of the intermembrane space interaction during chloroplast cell division.