The safety, effectiveness, and utility of medical nanorobotic devices will critically depend upon their biocompatibility with human organs, tissues, cells, and biochemical systems. In this Volume, we broaden the definition of nanomedical biocompatibility to include all of the mechanical, physiological, immunological, cytological, and biochemical responses of the human body to the introduction of artificial medical nanodevices, whether “particulate” (large doses of independent micron-sized individual nanorobots) or “bulk” (nanorobotic organs assembled either as solid objects or built up from trillions of smaller artificial cells or docked nanorobots inside the body) in form.