This trial will compare the efficacy and tolerability of 20 Hz vs. 1 Hz vs. sham repetitive transcranial magnetic stimulation targeting the dorsomedial prefrontal cortex, delivered twice daily over 15 days, in patients with a diagnosis of major depressive disorder. The trial will include structural and functional MRI, EEG, and behavioral measures obtained before, during, and after treatment.

Inclusion Criteria (Patient):

• Voluntary and competent to consent to treatment
• MINI confirmed diagnosis of MDD
• Outpatient
• Between the ages of 18-65
• Failed to achieve a clinical response to at least one pharmacotherapy or behavioral treatment in the current episode.
• Have had no increase or initiation of any psychotropic medication in the last 4 weeks prior to screening
• Must adhere to study assessment and intervention schedule.
• Pass the TMS Safety Screening Questionnaire.

Exclusion Criteria (Patient):

• Have a concomitant major unstable medical illness, cardiac pacemaker or implanted medical pump
• Have active suicidal intent
• Are pregnant
• Have a lifetime MINI diagnosis of bipolar I or II disorder, schizophrenia, schizoaffective disorder, schizophreniform, delusional disorder, or current psychotic symptoms have a MINI diagnosis of obsessive-compulsive disorder, post-traumatic stress disorder (current or within the last year), anxiety disorder (generalized anxiety disorder, social anxiety disorder, panic disorder), or dysthymia assessed by a study investigator to be primary and causing greater impairment than MDD
• Have received rTMS for any previous indication due to the potential compromise of subject blinding.