Seasonal affective disorder or SAD is a recurrent major depressive disorder with a seasonal pattern usually beginning in fall and continuing into winter months. A subsyndromal type of SAD, or S-SAD, is commonly known as "winter blues." Less often, SAD causes depression in the spring or early summer. Symptoms center on sad mood and low energy. Those most at risk are female, are younger, live far from the equator, and have family histories of depression, bipolar disorder, or SAD. Screening instruments include the Seasonal Pattern Assessment Questionnaire (SPAQ). Typical treatment includes antidepressant medications, light therapy, Vitamin D, and counselling. This paper provides an overview of SAD.