Although several pneumonia severity criteria have been firmly established, the exact definition of severe community-acquired pneumonia (CAP) remains elusive. Mortality from CAP remains high, reaching 50% in some series. The particular role of and spp. in severe CAP has been defined more clearly. Microbial diagnosis in the individual patient remains a difficult task. Despite promising new diagnostic tools, concerns about possible mixed origins preclude a change from the currently advocated broad-spectrum approach of antimicrobial treatment. Although there is some evidence that guidelines may optimize outcomes, their role in limiting the spread of resistance has only recently received attention. Finally, although there are promising data on the use of noninvasive positive pressure ventilation to treat pneumonia in patients without chronic obstructive pulmonary disease, its place in the management of acute respiratory failure remains to be defined in randomized studies.