The emergence and spread of bacteria resistant to multiple antibiotics is a complex, evolving, and alarming phenomenon that can lead to significant challenges in patient care, including therapeutic dead-ends, and threaten the advances of modern medicine. While progress has been made in controlling the spread of certain resistant bacteria (methicillin-resistant staphylococci, penicillin-resistant pneumococci, etc.), the situation is worsening for others: Enterobacteriaceae, with the growing spread of strains producing extended-spectrum beta-lactamases and the emergence of strains producing carbapenemases. (R.A.)