In this chapter, light therapy for mood disorders is discussed, including mood disorders during and after pregnancy. In the introduction, we discuss the symptomatology, etiology, and treatment of a specific type of mood disorder, seasonal affective disorder, since it kick-started the first clinical trials with light therapy. Second, we elaborate on the pathophysiology of mood disorders, in particular in the peripartum period. Next, we present an overview of the proposed working mechanisms of light therapy, followed by a discussion of the clinical trials that have followed after the initial research in seasonal affective disorder. Finally, we also focus on the limitations of these trials, such as considerable heterogeneity among studies and many methodological shortcomings. This is complemented by a number of suggestions for future research. Further studies are needed, which stems from the fact that the results have not always been consistent. Despite this, light therapy may be a promising treatment option for various types of mood disorders, since it shows a significant reduction in symptoms in many patients with few adverse effects.