Staphylococcus aureus is a Gram-positive opportunistic pathogen that has evolved a complex regulatory network to control virulence. One of the main functions of this interconnected network is to sense various environmental cues and respond by altering the production of virulence factors necessary for survival in the host, including cell surface adhesins and extracellular enzymes and toxins. Of these S. aureus regulatory systems, one of the best studied is the accessory gene regulator (agr), which is a quorum-sensing system that senses the local concentration of a cyclic peptide signaling molecule. This system allows S. aureus to sense its own population density and translate this information into a specific gene expression pattern. Besides agr, this pathogen uses other two-component systems to sense specific cues, and coordinates responses with cytoplasmic regulators of the SarA protein family and alternative sigma factors. These divergent regulatory systems integrate the various environmental and host-derived signals into a network that assures optimal pathogen response to the changing conditions. This chapter gives an overview of the most important and best studied S. aureus regulatory systems and summarizes the function of these regulators during host interactions. The regulatory systems discussed include the agr quorum-sensing system, the SaeRS, SrrAB and ArlRS two-component systems, the cytoplasmic SarA-family regulators (SarA, Rot and MgrA), and finally the alternative sigma factors (SigB and SigH).