Over the last decade, improvements in surgical techniques, lung preservation, immunosuppression, and management of ischemia–reperfusion injury and infections have contributed to increase the 1-year patient survival after lung transplantation to 70–80%(1). However, long-term survival is threatened by bronchiolitis obliterans, which is thought to be a form of chronic allograft rejection. Bronchiolitis obliterans after lung transplantation was first described in 1984 at Stanford University in heart–lung transplant recipients who showed a progressive decline in FEV1 (2). Lung biopsies from these patients showed intraluminal polyps comprised of fibromyxoid granulation tissue and plaques of dense submucosal eosinophilic scar. Obliteration of the small airways by these lesions produces progressive airflow obstruction, often accompanied by recurrent lower respiratory tract infection. Bronchiolitis obliterans, and its clinical correlate bronchiolitis obliterans syndrome, affect up to 50–60% of patients who survive 5 years after transplantation (3). In most patients, bronchiolitis obliterans is a progressive process that responds poorly to augmented immunosuppression, and it accounts for more than 30% of all deaths occurring after the third postoperative year (1). Survival at 5 years after the onset of bronchiolitis obliterans is only 30–40%, and survival at 5 years after transplantation is 20–40% lower in patients with than in patients without bronchiolitis obliterans (4). In this review, we present current concepts regarding post-transplant bronchiolitis obliterans, including:(1) the recently updated classification system for bronchiolitis obliterans syndrome (BOS),(2) an overview of current concepts regarding its pathogenesis and risk factors,(3) potential surrogate markers that may contribute to early detection, and (4) approaches to the management of this devastating complication.