As World War II drew to a close, the chief of the Army Air Forces turned to the director of Cal Tech's aeronautical laboratory, Theodore von Karman, to head a scientific advisory group whose first mission would be to peer 20 years into the technological future of air power. The resulting study, Toward New Horizons, foretold many of the developments of succeeding decades, including ballistic missiles, supersonic aircraft, and all-weather navigation and targeting, and won a well-deserved reputation for prescience and imagination. Fifty years later the chief of staff and the secretary of the air force sought a new version of von Karman's work. The result is a massive volume that includes both lucid descriptions of technology and recommendations for how to approach it -- including, provocatively enough, suggestions for areas that the air force should abandon (for example, exclusively military space-launch systems). The summary report is somewhat less useful than its 13 supporting monographs on such subjects as aircraft and propulsion systems, sensors, munitions, and information technologies. Blending a sense of practicality (the United States must be prepared for a failure rate greater than 50 percent in leading-edge technologies) with vision (an air force composed, in large part, of unmanned aircraft), the Scientific Advisory Board has discharged its mission well.