Over the last decade, improvements in surgical techniques, lung preservation, immunosuppression, and management of ischaemia/reperfusion injury and infections have made intermediate-term survival after lung transplantation an achievable goal. However, chronic allograft dysfunction in the form of bronchiolitis obliterans remains a major hurdle that threatens both the quality of life and long-term survival of the recipients. It affects up to 50-60% of patients who survive 5 yrs after surgery, and it accounts for >30% of all deaths occurring after the third postoperative year. This article discusses the alloimmune-dependent and -independent risk factors for bronchiolitis obliterans, the current understanding of the pathogenesis of bronchiolitis obliterans based on results of animal and human studies, the clinical staging of the complication, strategies that may contribute to the prevention and/or early detection of bronchiolitis obliterans, and suggestions for future research.