Graft-versus-host disease (GVHD) remains a major problem of allogeneic hematopoietic-stem cell transplantation (HSCT) and an obstacle for successful outcome. Clinically significant acute GVHD (grade II or higher) developed in 20 to 65 percent of the patients. Death due to this complication accounts for approximately 50 percent of the deaths that are not due to a relapse of the neoplasm. Up to 70 % of patients who survive beyond day 100 develop chronic GVHD and it is the leading cause of nonrelapse mortality more than 2 years after allogeneic HSCT. In addition, chronic GVHD is associated with decreased quality of life, impaired functional status, and ongoing need for immunosuppressive medications. The incidence of chronic GVHD is increasing because of expansion of the donor population beyond HLA-identical siblings, older recipient age, use of peripheral blood cells as the graft source, and infusion of donor lymphocytes for treatment of recurrent malignancy after HSCT. With the current rush in new findings related to GVHD, we see a significant advancement in its management. Given these various new options and challenges, it is important to identify the minimal requirements for diagnosis and treatment of GVHD, as access to the most sophisticated advances may vary depending on local circumstances (Tab. 4, Fig. 1, Ref. 51).