Nerves carry signals around the body and can be electrically stimulated for diagnostic and therapeutic purposes. However, the brain is difficult to stimulate non-invasively because of the high electrical resistance of the skull. Magnetic stimulation uses large pulses of magnetic field to induce currents in the brain without them having to pass through the skull. A UK invention, the technique is now widely used throughout the world. Tony Barker will describe the history of the technique, the physics principles on which it is based and some of its clinical applications, along with a practical demonstration.