This Symposium, held August 4-10, 1985 on the campus of Oregon State University in Corvallis, is the sixth of a series of international symposia concerned with broad aspects of the fixation of nitrogen gas by biological and chemical means. The first symposium of this series was held in Pullman, Washington (1974), the second in Salamanca, Spain (1976), the third in Madison, Wisconsin (1978), the fourth in Canberra, Australia (1980) and the fifth in Noordwij erhout, The Netherlands (1983). Prior to the organization of these symposia, small groups of usually no more than 10 or 12 of the now "old guard" in the field met in some obscure places, including Butternut Lake, Wisconsin, Sanabel Island, Florida and Camp Sage hen in California, to discuss developments in the field. Concern about an energy crisis in the nineteen seventies served as an impetus for the organization of workshops and preparatiol. of publications urging government agencies to provide funds for the support of several neglected areas in the field, including the genetics of nitrogen-fixing organisms and the biology of Frankia. In looking back, it becomes apparent that there have been drastic changes in the extent of research support in the field and in the contents of the programs of the continuing series of symposia.