The depressive aspect of bipolar disorder is often overlooked, possibly due to its less dramatic nature, despite its significant impact on the lives of those affected. Bipolar depression (BPAD-DP) is associated with a twenty fold increased risk of suicide, and typically lasts three to five times as long as a manic or hypomanic episode. Despite this, there has been relatively sparse investigation of treatments for BPAD-DP, with guidelines based primarily on expert judgment rather than clinical trials. In addition a significant proportion of patients with bipolar depression do not respond to the range of commonly used medications. One of the only substantially new treatments developed for unipolar depression in recent years has been the advent of repetitive transcranial magnetic stimulation (rTMS). Repetitive TMS has been evaluated in over 20 trials conducted over the last ten years, but no substantive trials have explored its use in bipolar depression. We propose to do this, conducting a large scale clinical trial. The trial will include the assessment of both high frequency left sided rTMS (as there is clearly the greatest evidence for the effectiveness of this in unipolar depression) and low frequency right sided rTMS (as this there is growing evidence of the effectiveness of this in unipolar depression and we have an excellent pilot study to suggest its potential in BPAD-DP and it has never previously been assessed in a clinical trial exclusively targeting this patient group). Our previous research strongly supports the effectiveness of rTMS paradigms including low frequency right-sided stimulation in unipolar depression and suggests these may have value in BPAD-DP. As BPAD-DP is clearly a clinical problem of significant impact and with limited treatment options, there is a pressing need for the development and definitive testing of novel treatments such as rTMS.