Human Spaceflight: Apollo 50 Years On summarizes the 2019 National Academies of Engineering Annual Meeting plenary presentations and forum. The Annual Meeting celebrated not only the 50th anniversary of the Apollo 11 mission but human spaceflight in general, from the first ventures beyond Earth's atmosphere to future flights to the Moon, Mars, and beyond. Speakers reflected on the inspiring trajectory of ingenuity, achievements, and lessons of the Apollo mission and discussed implications for future exploration, workforce development, and public engagement.