In recent years two techniques have become available to stimulate the human brain noninvasively through the scalp: repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS). Prolonged application of either method (eg, several hundred TMS pulses [rTMS] or several minutes of tDCS) leads to changes in excitability of the cortex that outlast the period of stimulation. Because of this, besides the implications for experimental neuroscientists, there is increasing interest in the potential for applying either method as a therapy in neurology, psychiatry, rehabilitation, and pain. Given that both techniques lead to the same final result, this article discusses in theory several issues that can help an investigator to decide whether rTMS or tDCS would be more suitable for the scope of the planned work.