Pneumonia is an important cause of morbidity and mortality in the United States. The provision of effective prophylaxis for pneumonia has become a major goal for both public health officials and individual physicians. Prophylaxis for community-acquired pneumonia is pathogen-specific and is directed toward the most common microorganisms that cause it. The 23-valent pneumococcal polysaccharide vaccine; the trivalent influenza vaccine; the Haemophilus b conjugate vaccine; and either trimethoprim-sulfamethoxazole, dapsone, or aerosolized pentamidine are recommended to prevent Streptococcus pneumoniae, influenza viruses, H. influenzae type b, and Pneumocystis carinii respectively. Except for the microorganisms listed above, the prevention of nosocomial pneumonia is not pathogen-specific. Rather, prevention of nosocomial pneumonia requires the use of infection control procedures, including patient and staff education; isolation of patients with highly contagious respiratory pathogens; vigorous hand washing; cleaning and sterilizaton of respiratory equipment; and use of sterile water in nebulizers and humidifiers. It also requires procedures to limit pooling and aspiration of secretions, such as positioning and rotation of the bed-bound patient; frequent suctioning of respiratory secretions using gloves and sterile suction catheters; and limiting enteral alimentation. Finally, selective decontamination of the digestive tract may be considered for intubated patients.