Enterobacteriaceae are a large, diverse group of facultative Gram-negative rods, recovered as natural inhabitants of the environment and the large intestines of humans and animals. They are important pathogens in healthcare- and community-associated infections in the United States and worldwide. The spectrum of infections includes bacteremias, pneumonias, surgical site infections, and urinary tract infections. Patients at greatest risk include those in medical and surgical intensive care units and residents of short- and long-term acute care hospitals. Infants, the elderly, the immunocompromised, and those with extensive exposure to healthcare are the most vulnerable. In developing countries they are among the leading cause of diarrheal disease and death of children under age 5. Increasing antibiotic resistance to third-generation cephalosporins, fluoroquinolones, and carbapenems results in diminished treatment choices for the prevention and management of both healthcare- and community-associated infections. Several members of this group may also be used to launch biological weapons. Strategies for prevention include healthcare personnel education and training, checklists, surveillance, and zero tolerance for noncompliance with evidence-based best practices. Adoption and monitoring of patient and quality improvement outcomes are essential to reducing infections and developing a culture of patient safety.