Transcranial Magnetic Stimulation (TMS) is a new non-invasive method to investigate the central nervous system. Initially it was used to assess the functional integrity of the pyramidal pathways but more recently various other aspects of brain function have been studied including cortical excitability. By localised interference with brain function, it is possible to use TMS to assess the relationship between various brain regions and cognitive functions. The therapeutic effect of TMS has been explored in the treatment of neurological diseases and psychiatric disorders such as epilepsy, cerebellar ataxia and depressive illness.