 This is a double-blind, randomized, sham-controlled phase II study of the effects of Low Field Magnetic Stimulation LFMS on brain circuitry of adults with treatment-resistant Major Depressive Disorder MDD. Eligible subjects will be randomly assigned to double-blind treatment with three 20 minute sessions of either 1 active LFMS or 2 sham LFMS. Resting state fMRI will be performed at baseline and following the third and final treatment session. 