The subject of this chapter is bioartificial organs. The concept of the immunoisolation of transplanted cells is given along with a summary of key immunological concepts. The permeability properties of immunoisolation membranes are also described. For the bioartificial pancreas, several approaches are discussed in some detail. These include intravascular devices with and without ultrafiltration, microencapsulation, and macroencapsulation. A pharmacokinetic model of glucose regulation in the body is given, and this is used to describe the efficacy of a bioartificial pancreas for treating diabetes. The bioartificial liver and the bioartificial kidney are also discussed in this chapter.