This volume of Frontiers of Engineering presents papers on the topics covered at the National Academy of Engineering's 2019 US Frontiers of Engineering Symposium, hosted by Boeing in North Charleston, South Carolina, September 25-27. At the annual 2 1/2-day event, 100 of this country's best and brightest early-career engineers - from academia, industry, and government and a variety of engineering disciplines - learn from their peers about pioneering work in different areas of engineering. Frontiers of Engineering conveys the excitement of this unique meeting and highlights innovative developments in engineering research and technical work.