Transcranial magnetic stimulation (TMS) is a technique for noninvasive stimulation of the human brain. Stimulation is produced by generating a brief, high-intensity magnetic field by passing a brief electric current through a magnetic coil. The field can excite or inhibit a small area of brain below the coil. All parts of the brain just beneath the skull can be influenced, but most studies have been of the motor cortex where a focal muscle twitch can be produced, called the motor-evoked potential. The technique can be used to map brain function and explore the excitability of different regions. Brief interference has allowed mapping of many sensory, motor, and cognitive functions. TMS has some clinical utility, and, because it can influence brain function if delivered repetitively, it is being developed for various therapeutic purposes.