Hospital-acquired pneumonia (HAP) is the second most common nosocomial infection in acute care hospitals, with an estimated attributable mortality of 27% to 50%. Although the highest prevalence is among ventilated patients, pneumonia also occurs far too frequently in non-ventilated patients. Poor oral hygiene, especially in the critically ill, has been established as a significant risk factor. Changes in the chemistry and physiology of the oral cavity along with exposure to respiratory pathogens within hours of entering the intensive care unit (ICU) set the stage for bacteria-infested biofilm formation on the surfaces of teeth as well as the tongue, gingival crevices and other mucosal surfaces. These bacterial reservoirs stand ready to disperse pathogens for aspiration into the lungs where they can initiate infection. In fact, the CDC has stated that in 76% of ventilator-associated pneumonia (VAP) cases, the bacteria colonizing the mouth before pneumonia is diagnosed are the same as those causing the pneumonia. In this course we discuss the relevant alterations in oral physiology, phases of biofilm formation, means of pathogen colonization and the mechanisms of their aspiration, together with recognized oral care recommendations to be implemented as pneumonia preventative measures.