Postoperative infection and hospital-acquired infections are not prevented by antibiotic use.  The key to maintaining acceptable post-operative infection rates and preventing hospital-acquired infections is adherence to strict aseptic technique and biosecurity/infection control. Antibiotic use is justified in surgery if the appropriate class, dose, route and timing of the antibiotic administration is followed. During this lecture, we will discuss the factors that influence postoperative infection risk, the essential components of the aseptic technique (and why it is so important), and the rational selection of antibiotics – when they are justified and when they are not.