In 1995, the National Academy of Engineering initiated the Frontiers of Engineering Program, which brings together about 100 young engineering leaders at annual symposia to learn about cutting-edge research and technical work in a variety of engineering fields. The 2009 U.S. Frontiers of Engineering Symposium was held at The National Academies' Arnold O. and Mabel Beckman Center on September 10-12. Speakers were asked to prepare extended summaries of their presentations, which are reprinted in this volume. The intent of this book is to convey the excitement of this unique meeting and to highlight cutting-edge developments in engineering research and technical work.