Chronic graft-versus-host disease (GVHD) remains a vexing and dangerous complication of allogeneic stem cell transplantation. Mild forms of chronic GVHD are often manageable with local or low-dose systemic immunosuppression and do not affect long-term survival. In contrast, more severe forms of chronic GVHD require intensive medical management and adversely affect survival. This report reviews current concepts of the pathogenesis, clinical risk factors, classification systems, organ manifestations, and available treatments for chronic GVHD. It also provides a comprehensive listing of the published clinical trials aimed at prevention and primary treatment of chronic GVHD.