The Chemistry Center for Combating Antibiotic Resistant Bacteria (CC4CARB) is a NIH NIAID lead initiative. CC4CARB is an innovative chemistry center focused on the synthesis and delivery of rationally designed focused libraries to the scientific community for use in Gram-negative antibacterial drug discovery programs. The ultimate objective of CC4CARB is to combine these libraries and create a large collection of chemical matter specifically targeting Gram-negative antimicrobial drug discovery.