Major depression (or MDD) in adolescents is a major public health problem. MDD affects approximately 15% of adolescents; it is associated with impairment in social, family, and academic functioning, and it is a major risk factor for suicide - a leading cause of death in adolescents . Unfortunately, there is a paucity of treatment options for this age group. Selective serotonin reuptake inhibitors (SSRIs) are the only class of medications approved for treating MDD in adolescents, but rates of remission following treatment with SSRIs are only 30 to 45 percent. Cognitive behavior therapy is associated with similar remission rates and access is limited. Most adolescents will require more than one therapeutic intervention in order to achieve full symptom control. Collectively, there is overwhelming evidence that additional treatment options are urgently needed to improve outcomes for teens with MDD. One novel treatment for adolescent MDD is repetitive transcranial magnetic stimulation (rTMS). Studies in children have been limited (a total of 23 cases). This is surprising given the evidence suggesting younger adult subjects with MDD respond better to rTMS (56% response rate) than older subjects. This limited experience with rTMS for adolescent MDD represents a substantial gap in the knowledge, recently recognized in publications calling for further study of rTMS in adolescent depression. Most importantly, the mechanism of action of rTMS in adolescent MDD is not well understood. The objective of this application is to develop an understanding of the brain alterations associated with the positive clinical changes that occur with rTMS in adolescent MDD. Such knowledge will provide the basis for pursuing rTMS for adolescent MDD as a rational therapeutic technique.