Molecular nanotechnology is a rapidly emerging field that will allow for the precise and purposeful arrangement of matter atom by atom and eventually the building of submicron-scale medical sensors and therapeutic devices. These tools will provide the means to analyze, understand, and precisely control the molecular machinery of the human body. This will allow for the detection and correction of any undesired structural changes (disease or aging) at the finest level of detail and the earliest possible time. Genuine rejuvenation followed by the indefinite maintenance of an optimal physiologic state, or molecular homeostasis, may ultimately become possible. Current progress is rapid and accelerating, with a wide array of early nanoscale medical technologies under active development at the present time.