Intraabdominal infections are a wide range of diseases that include penetrating abdominal trauma, appendicitis, peritonitis, and abscess. Most are polymicrobic, involving aerobic and anaerobic bacteria. The primary treatment is surgery, but important issues regarding administration of antimicrobials may affect patient outcome. Evaluation of an antimicrobial regimen must include consideration of outcomes—survival, organ failure, adverse drug effects, and superinfection. Single‐agent regimens have demonstrated benefit in patients with acute intraabdominal contamination and established infections. Guidelines for selecting antimicrobial agents are available from the Surgical Infection Society. Regimens are effective when active against most bacteria isolated from the focus of abdominal infection. The patient's clinical response, not culture results independent of clinical findings, is the primary guide for directing changes in ther