Chronic graft-versus-host disease (cGVHD) is a common and difficult complication of allogeneic transplantation. Advances have been hindered by a lack of uniform criteria for diagnosis and staging and by a lack of high quality prospective studies. In six articles, consensus criteria are proposed for clinical and histological diagnoses and response assessments for cGVHD. Recommendations are also made for the study of biomarkers in cGVHD, for ancillary management and supportive care of patients with cGVHD and for the design of clinical studies. The recommendations and criteria proposed by the consensus group are likely to facilitate and profoundly alter the management and study of cGVHD.