In the United States, healthcare acquired infections (HAIs) or nosocomial infections are the sixth leading cause of death. This article reviews the history, prevalence, economic costs, morbidity and mortality, and risk factors associated with HAIs. Types of infections described include bacterial, fungal, viral, and multidrug resistant infections that contribute to the most common causes of HAIs, which include catheter- associated urinary tract infections, hospital-acquired pneumonias, bloodstream infections, and surgical site infections. Most nosocomial infections are preventable and monitoring and prevention strategies are described.