The Combined Volume, Third Edition of A Course in Miracles is the only edition that contains in one place all of the writings that Dr. Helen Schucman, its Scribe, authorized to be printed.  It is published soley by The Foundation for Inner Peace, the organization chosen by Dr. Schucman in 1975 for this purpose. 
This Combined Volume also includes the Supplements to A Course in Miracles: "Psychotherapy: Purpose, Process and Practice" and "The Song of Prayer."  These sections are extensions of the Course principles, whcih were dictated to Dr. Schucman shortly after she completed A Course in Miracles.