Recently clinical guidelines categorize pneumonia in to three types: community, healthcare-associated, and hospital-acquired. Much of the existing research to describe the epidemiology of pneumonia in critically ill patients comes from single-center studies or from retrospective database analyses, which limit generalizability and lead to over-prescription of broad-spectrum antibacterial agents. This will be a prospective, multicenter epidemiological study to characterize pneumonia epidemiology in critically ill adult patients.