Allogeneic tissue transplantation is one of the most effective treatments for several diseases and injuries, in particular, malignant and non-malignant hematological conditions.Following this procedure, transplanted tissue encounters various complications, one of the most serious being graft-versus-host disease (GvHD). The management of GvHD directly affects the success of transplantation and the survival rate of the patient; therefore, many studies have focused on GvHD prevention and control. This review briefly explains the transplantation process, causes of graft rejection, and importance of the human leukocyte antigen system. Initially, we address the pathophysiology and immunobiology of GvHD, the cells involved in this complication, the differences between chronic and acute GvHD, and the importance of graft-versus-leukemia. Interestingly, various types of immune cells are involved in GvHD pathogenesis. After explaining how these cells affect the GvHD process, we discuss the studies conducted to control and reduce GvHD symptoms.