The purpose of this Chapter is to give the reader a broad overview of the human pathogen Staphylococcus aureus. The Chapter will focus on several aspects of this organism in relation to the problems it causes in the healthcare setting. Staphylococci are the topic of an extensive literature and many books. As a consequence, the information here will not deal with any particular subject in great depth, but will point the reader to literature which will aid in their accessing an understanding of the more important aspects of S. aureus biology. We will provide a short general introduction and then examine aspects of which infections S. aureus cause and how they cause them. The issue of bacterial resistance to antibiotics will be discussed and the latter half of the Chapter will deal with hospital-acquired S. aureus infections and the more recent advent of community-acquired MRSA. Finally, information on current treatments for staphylococcal infections will be presented, incorporating new and proposed treatments.