Objective: While there has long been interest in any nutritional contribution to the onset and treatment of mood disorders, there has been increasing scientific evaluation of several candidate nutritional and dietary factors in recent years. In this paper, we overview research into any vitamin D insufficiency and deficiency contribution to depression. Method: The relevant literature was reviewed. Results: Cross-sectional studies have identified associations between depression and low vitamin D levels, but studies have failed to clarify whether vitamin D deficiency is an antecedent cause, correlate or consequence of depression. While vitamin D deficiency and insufficiency have been linked with seasonal affective disorder, suggested associations have not been rigorously tested. There has been insufficient research to establish whether and when vitamin D supplementation should be considered as an augmentation strategy with antidepressant drugs. Conclusion: There is currently insufficient evidence to argue strongly for vitamin D supplementation in patients with depression, but such a strategy is worthy of consideration in depressed patients whose lifestyle and geographical residence may indicate a risk of vitamin D insufficiency - or where low vitamin D levels have been quantified.