Abstract Staphylococcus aureus is a leading cause of human morbidity and mortality, causing infection of the skin and soft tissues, post-surgical wounds, and lung infection among influenza and cystic fibrosis patients. Widespread multi-drug resistance has made eradication of S. aureus increasingly challenging, necessitating a deeper understanding of the physiology and pathogenesis associated with these organisms. A key aspect of bacterial survival and adaptation to altered environmental conditions is the ability to rapidly alter cellular behavior through second messenger signal transduction. C-di-AMP has recently emerged as a key regulator of bacterial physiology, pathogenesis, and immune activation. In the context of S. aureus, we believe that c- di-AMP produced by S. aureus has three important roles; (i) as a signaling molecule that mediates S. aureus metabolism and antibiotic resistance, (ii) as a bacterial PAMP that promotes pathological inflammation and host susceptibility to bacterial infection, and (iii) as a mediator of inter-bacterial signaling that alters the outcome of co-infections. Findings from these studies may have significant impacts on the course of antibiotic therapy during S. aureus infection and may uncover a novel target to eradicate recalcitrant S. aureus and the inflammation itpromotes.