The first studies of seasonal affective disorder (SAD) began to appear in the psychiatric research literature in 1984 with the influential article by Norman Rosenthal and colleagues at the National Institutes of Mental Health. In 1987, the Diagnostic and Statistical Manual of Mental Disorders (3rd ed., rev.; DSM-III-R; American Psychiatric Association, 1987) included a "seasonal pat tern" modifier for diagnoses of major depression and bipolar disorder (including not otherwise specified ver sions of both disorders). Subsequent editions of the DSM also included an optional modifier for these diagnoses (DSM-IV-American Psychiatric Association, 1994; DSM-IV-TR-American Psychiatric Association, 2000; DSM-5-American Psychiatric Association, 2013). Regardless of DSM edition, the basic criteria for diagnosing seasonal pattern are meeting the diagnostic criteria for major depression and experiencing recurrences that cor respond to particular seasons. The most commonly reported pattern is that of symptoms emerging in the fall and winter and remitting in the spring and summer. The close correspondence in time between the emer gence of SAD in the psychiatric literature and the inclusion of a seasonal pattern modifier in DSM-III-R sug gests that the research base for major depression with seasonal pattern was a small number of SAD studies (Hansen, Skre, & Lund, 2008). Following their meeting with Rosenthal and his research colleague, Michael Terman, Robert L. Spitzer, chair of the Work Group to Revise DSM-III, and Janet B. W. Williams, text editor, reported that the seasonal pattern modifier was included in DSM-III-R (Spitzer & Williams, 1989). Seasonal pattern had not been considered by the DSM-III-R Mood Disorders Advisory Committee. The inclusion of the seasonal pat tern modifier was justified because it was considered to be more diagnostically valid than other included mood diagnoses, such as melancholia and dysthymia. Consideration was given to creating a separate diagnosis for SAD, but this idea was rejected because it would have