Transcranial Magnetic Stimulation (TMS) is an exciting new technology that along with repetitive TMS (rTMS) offers the potential to explore and understand brain-behavior relationship in a way that builds on recent advances in functional neuroimaging (ie, PET, SPECT, fMRI imaging). rTMS as a relatively noninvasive probe of cortical function provides an opportunity to explore the relationships between regional brain activity and symptomatology across psychiatry illnesses. In this article we briefly review the current thinking regarding the neurobiology of mood and the effects of rTMS on mood in healthy and depressed subjects.