The long-term future envisioned by nanomedicine researchers includes incredibly tiny therapeutic agents that smartly navigate under their own power to a specific target—and only that target—anywhere in the body. On arrival, these self-guided machines may act in any number of ways—from delivering a medicinal payload to providing real-time updates on the status of their disease-fighting progress. Then, having achieved their mission, they will safely biodegrade, leaving little or no trace behind. These so-called nanobots will be made of biocompatible materials, magnetic metals or even filaments of DNA: all materials carefully chosen for their useful properties at the atomic scale, as well as their ability to slip past the body's defenses undisturbed and without triggering any cellular damage.