The burden of pneumonia, including that due to respiratory viruses, is markedly higher in the very young (<5 years) and older adults (≥50 years). Respiratory viruses substantially contribute to pneumonia in both adults and children, and when systematically tested for, are more commonly detected than bacteria in both adults and children. It is difficult to distinguish between viruses by clinical presentation, and the exact clinical implication of viral detections among patients with pneumonia depends on the pathogen detected; however, there is increasing evidence of their importance in pneumonia.