The tragic events of September 11, 2001, have forever changed the lives of the individuals and families that were directly affected and have changed history for everyone. Those same events were the beginning of a 24-hour-per-day, 7-day-per-week effort by structural engineers to investigate the condition of the buildings remaining at the World Trade Center site, to work with the rescue and clean-up crews in evaluating the safety of the towering piles of rubble, and to try to explain what happened to the buildings as they collapsed. After 9-11 describes one engineer’s experiences on site and off as part of that effort.