Community-acquired pneumonia (CAP) remains a major cause of morbidity and mortality in the United States. The ideal of a simple diagnostic evaluation yielding a specific etiologic diagnosis allowing directed antimicrobial therapy remains elusive. Empiric therapy is justified as initial management, as the specific bacteriological etiology of most cases of CAP is usually unknown, and delaying therapy while attempting to find a diagnosis may be injurious to the patient. Guidelines have been developed to assist in the recognition and evaluation of CAP based on age and underlying medical illness as predictors of outcome. While these criteria are by no means perfect and cannot be applied to every individual, they offer a rational approach to the initial management of the patient.