Abstract Bipolar depression is poorly understood and researched, yet it is has a huge impact on functioning in bipolar disorder. This review explores the current status of research regarding the phenomenology, natural history, neuropsychology, psychosocial predictors and cognitive style of bipolar depression. The current status of pharmacotherapy and psychological treatment of bipolar depression is also described. In particular, the manner in which cognitive behaviour therapy for bipolar depression has been adapted from CBT for unipolar depression is critically evaluated. It is concluded that there appears to be a considerable overlap between the features of unipolar and bipolar depression, yet there is also emerging evidence for specific elements. The ability of current psychological theories of bipolar disorder to account for the findings are compared, and as a consequence, a new preliminary integrative model is proposed to direct future hypothesis-led research, which will need to incorporate more suitable populations and utilise more objective methods of assessment.