Operative wound infection is examined through classifications based on estimation of frequency, severity, and sources of infection. These classifications help in identifying preventive and corrective measures. All surgeons are concerned with postoperative infection because it can convert a superior technical result into a disaster. The analysis of postoperative infection is complicated by the complex and constantly changing relations among host, challenging microbe, and the existing antimicrobial measures. The effect of physical, pharmacologic, and biological variables is estimated with emphasis on measures that promise further control of infection in the surgical patient. Proposals are offered for further efforts in controlling this hazard.