Transcranial magnetic stimulation (TMS) is a noninvasive neuromodulation technique based on the application of powerful and rapidly changing magnetic fields on the skull surface that generate targeted electrical currents in the brain, painlessly and without the need for surgery, anesthesia, or the induction of seizures. Since its development in the mid-1980s, it has become a widely used tool for neuroscience research and clinical applications, both diagnostic and therapeutic. In 2008, the US Federal Drug Administration approved the use of high-frequency repetitive TMS over the left dorsolateral prefrontal cortex for the treatment of major depressive disorder, and in 2013 the use of deep TMS H-coils was also approved for the same indication. In the present chapter, we will review the principles and clinical applications of TMS, with a focus on antidepressant therapy.