Bipolar patients generally spend much more time in the depressed phase of their illness than the manic phase, and there are many more bipolar type II and bipolar spectrum disorder patients than there are bipolar type I. Additionally, there is a significant risk of suicide in bipolar patients when depressed. The treatment of the depressed phase of bipolar disorder is therefore a matter of some priority. Here, we review current evidence supporting the use of five groups of treatments: anti-depressants; lithium; anti-convulsants (valproate, and carbamazepine, lamotrigine, gabapentin); anti-psychotics; and other treatments (electroconvulsive therapy, benzodiazepines, sleep-deprivation, and dopamine agonists). From this review, it is apparent that the literature regarding the treatment of bipolar depression is significantly limited in several key areas. Nonetheless, from the evidence currently available, the treatments with the best evidence for efficacy are selective serotonin reuptake inhibitors (SSRIs) and lamotrigine. There is also some evidence in favour of bupropion and moclobemide. Although lithium and olanzapine monotherapies can also be beneficial, they appear less efficacious than antidepressants. One of the major concerns about treatment with antidepressants has been the risk of precipitating a switch into mania. However, recent studies suggest that, if a mood stabilizer and antidepressant are given concurrently, then the risk of switching is minimized. There is also recent evidence for an independent antidepressant action for at least one atypical antipsychotic. Therefore, the conclusion from this review, in contrast to previous suggestions, is that a combination of an atypical antipsychotic and either an SSRI or lamotrigine may provide a useful first-line treatment for depressed bipolar disorder patients. Further research is clearly required to examine this approach and compare it with other possible treatment options.