This volume includes 14 papers from the National Academy of Engineering's Ninth Annual U.S. Frontiers of Engineering Symposium held in September 2003. The U.S. Frontiers meeting brings together 100 outstanding engineers (ages 30-45) to learn from their peers and discuss leading-edge technologies in a range of fields. The 2003 symposium covered these four areas: environmental engineering; fundamental limits of nanotechnology; counterterrorism technologies...