shortage of donor organs. Xenotransplantation using pigs as donors offers the possibility of resolving the current crisis in the supply of cadaveric human organs. Although there have been reported severe immunologic response to swine organs, much progress has been made in the past decade largely because of the understanding the xenoimmunobiology of pig-to-nonhuman primate transplantation and the increasing availability of pigs that have undergone genetic modifications such as alpha 1,3-galactosyltransferase gene (GalT-KO swine). The results of preclinical transplantation of pig organs or cells(graft survival: heterotopic heart> 500 days; life-supporting kidney90 days; islets＞180 days)have been encouraging when combined with a strategy to induce tolerance or a use of co-stimulatory blockage. In this review, we discuss immunologic barriers to xenotransplantation and recent attempts to overcome them, strategies to induce tolerance across a xenogenic barrier, and progress towards xenotransplantation as a clinical therapy.