In 2008 a committee of distinguished engineers, scientists, entrepreneurs, and visionaries set out to identify the most important, tractable engineering system challenges that must be met in this century for human life as we know it to continue on this planet. For the forum at the National Academy of Engineering's 2015 annual meeting, 7 of the 18 committee members who formulated the Grand Challenges for Engineering in 2008 reflected on what has happened in the seven year since. Grand Challenges for Engineering: Imperatives, Prospects, and Priorities summarizes the discussions and presentations from this forum.