The science of transferring a graft from one part of the body to another or from one individual, the donor, to another, the recipient. The graft may consist of an organ, tissue, or cells. If donor and recipient are the same individual, the graft is autologous. If donor and recipient are genetically identical (monozygotic), it is syngeneic. If donor and recipient are any other same-species individuals, the graft is allogeneic. If the donor and recipient are of different species, it is called xenogeneic.