As the field of solid organ transplantation has grown, so has the importance of infectious complications in this select group of patients. Chronic immunosuppression compromises the natural host defenses that typically prevent lower respiratory tract infections and makes the solid organ transplant recipient especially susceptible to pneumonia. Evaluation of pneumonia in this population differs owing to the potential for opportunistic infections. Lung transplant recipients are particularly susceptible to pneumonia and pose unique diagnostic dilemmas. An understanding of the time line for the different key pathogens after transplantation aids the initial evaluation and management.