Nosocomial pneumonia remains a significant cause of hospital-acquired infection, imposing substantial economic burden on the health care system worldwide. Various preventive strategies have been increasingly used to prevent the development of pneumonia. It is now recognized that patients with health care–associated pneumonia are a heterogeneous population and that not all are at risk for infection with nosocomial pneumonia pathogens, with some being infected with the same organisms as in community-acquired pneumonia. This review discusses the risk factors for nosocomial pneumonia, controversies in its diagnosis, and approaches to the treatment and prevention of nosocomial and health care–associated pneumonia.