The two fundamental criteria for successful cell transplantation in the adult mammalian brain are, first, the selection of an appropriate donor tissue at a stage of development when it can survive and grow after transplantation, and, second, the selection of an implantation method and site within the host brain where the graft can be nourished, vascularized, and rapidly incorporated into the host environment (Stenevi et al., 1976). The first of these topics is addressed in the first seven chapters of the present volume, in which the selection, collection, dissection, and handling of embryonic tissues, cell lines, engineered cells, and artificial devices for implantation are each considered in some detail. The second section, introduced by the present chapter, considers the alternative methods of implantation available for transfer of the graft tissues into the nervous system of the host animal.