Bacteria are said to be multidrug-resistant (MDR) when, due to the accumulation of acquired resistance to several classes of antibiotics, they are sensitive to only a small number of antibiotics that can be used therapeutically. Multidrug resistance is a step toward a therapeutic dead end. It affects bacteria causing community-acquired infections (e.g., pneumococci, tuberculosis bacilli) and bacteria causing nosocomial infections. The fight against MRB in hospitals, which is part of a comprehensive policy for the prevention of nosocomial infections (NI) and the control of antibiotic resistance, is a national priority that involves the entire hospital community and is included in activity and quality indicators, as well as in accreditation standards for healthcare facilities. Due to their high prevalence, pathogenic potential, commensal nature—which poses a risk of spread outside the hospital—clonal nature, and the easily transferable nature of the resistance mechanisms involved, the MRBs covered by the national program and this summary are methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum beta-lactamase-producing Enterobacteriaceae (ESBL-producing Enterobacteriaceae). (R.A.)