Artificial limbs are familiar devices to replace body parts lost to injury or illness, but brain implants that can command those limbs to work represent a revolutionary advance. By creating a direct line of communication from the brain to the prosthetic device, neurally-controlled chips not only restore functionality, but also recreate the sensory experience of the lost limbs. A Manhattan Project for prosthetics, the work requires interdisciplinary collaboration across the fields of applied physics, engineering, neurophysiology, computer programming, and clinical science. How far can researchers go with these implants? How will the work inform robotics and neuroscience?