Nerves carry signals around the body and can be electrically stimulated for diagnostic and therapeutic purposes. However, the brain is difficult to stimulate because of the high electrical resistance of the skull. Magnetic stimulation uses large pulses of magnetic field to induce currents directly in the brain. A UK invention, the technique is now widely used throughout the world. Tony Barker will describe the history of the technique, its physics principles, some clinical applications, and give a practical demonstration.