"Mesoscopic physics" refers to the physics of structures larger than a nanometer (one billionth of a meter) but smaller than a micrometer (one millionth of a meter). This size range is the stage on which the exciting new research on submicroscopic and electronic and mechanical devices is being done. This research often crosses the boundary between physics and engineering, since engineering such tiny electronic components (as many as one million transistors can be fitted onto a single chip) requires a firm grasp of quantum physics. Applications for the future may include such wonders as microscopic robot surgeons that will travel through the blood stream to repair clogged arteries; submicroscopic actuators and builders; and supercomputers that fit on the head of a pin.