The above statement was made by Guido Persijn, former Medical Director of the Eurotransplant Foundation, an international organisation that coordinates organ donation and transplantation. Xenotransplantation is the transplantation of organs, tissues or cells from one species of animal to another. This chapter will look at transplantations between animal and humans. Xenotransplantation is one possible solution for the organ donor shortage in the area of transplant medicine77. However, there is still a ban on this type of procedure because of the lack of clarity about the sort of risks entailed. The natural rejection responses to cross–species components still create insurmountable problems. The transfer of viral DNA with, as yet, unpredictable consequences is also another matter that requires due attention. The various facets of this topic will be discussed in this chapter, as will the question of whether or not xenotransplantation is ethically responsible. We’ll begin with the history of xenotransplantation, which has its origins in a dark past.