Book excerpt: The matching of airline passenger info. against terrorist watchlist records is a frontline defense against acts of terrorism that target the our civil aviation system. Passengers identified as matches to the No-Fly list are prohibited from boarding commercial flights, while those matched to the Selectee list are required to undergo additional screening. The TSA has developed an advanced passenger prescreening program -- known as Secure Flight -- that matches passenger info. against terrorist watchlist records. This report discusses the challenges the program has faced, incl.: protecting passenger privacy, completing performance testing, fully defining and testing security requirements, and establishing reliable cost and schedule estimates, among other things.