Seasonal Affective Disorder (SAD) is a form of major depression that recurs at the same time every year, in the late autumn-winter months. The causes of SAD are not entirely known, though it is believed that the change in the availability of sunlight is the trigger. Statistics show that SAD becomes increasingly common the farther people live north or south of the equator, and episodes tend to be longer and more severe at higher latitudes. The current standard treatment for SAD is light therapy, in which the client uses a very bright light box for up to 90 minutes a day. This treatment is plagued by high discontinuation and relapse rates. In addition, between 45% and 55% of sufferers, especially those with severe depressive symptoms, never benefit from light therapy at all. In the author's studies, CBT in addition to light therapy had a 60% success rate a year out from the treatment, compared to a 100% relapse rate for light therapy alone. This therapist guide presents an evidence-based group treatment for SAD. In 12 sessions over 6 weeks, participants learn the traditional CBT elements of behavioural activation and cognitive restructuring to improve coping with the winter season. Some cognitive restructuring focuses on challenging negative thoughts related to the winter season, weather conditions, and lack of light. A relapse-prevention component addresses early identification of negative anticipatory thoughts about winter and SAD-related behaviour changes, how to use the skills learned to cope with subsequent winter seasons, and the development of a personalized relapse-prevention plan. The corresponding workbook provides homework exercises, monitoring forms, and other useful components to supplement the work done in therapy.