To understand the etiology of seasonal affective disorder (SAD) heterogeneous biological, psychological and environmental mechanisms needs to be considered. The aim of our study was to review theoretical hypotheses and therapeutic possibilities for seasonal affective disorder, which focus on alterations of circadian rhythms and monoaminergic neurotransmitter function as well as the role of vitamin D3 and possible implications of the cognitive-behavioral model. These discrepant hypotheses are insufficient alone to interpret the pathophysiology of SAD, but the integrative dual vulnerability hypothesis is an option to explain emergence of seasonal affective disorder. In addition to summarizing theoretical approaches we also review and evaluate the therapeutic possibilities derive form these hypotheses. In practice the most effective treatment for SAD is the combination of light therapy, antidepressants and psychotherapy.