The report contains papers presented at the Sixth AFOSR Symposium on Advanced Propulsion Concepts, held at the Bell Aerospace Company, Niagara Falls, New York, 4-6 May 1971. Papers are directed toward providing an assessment of current research involving advanced propulsion concepts, and to systems forecasting from the viewpoint of science and engineering middle-management in aerospace industry, Federal agencies and Department of Defense laboratories. Symposium sections emphasized turbine and ramjet propulsion; air augmented rockets; chemical rockets and hybrids, solid and liquid; space power; nuclear propulsion; and electric propulsion. Volume 2 is classified. (Author).