Until recently, the Transportation Security Administration (TSA) had applied relatively uniform methods to screen airline passengers, focusing primarily on advances in screening technology to improve security and efficiency. TSA has recently shifted away from this approach, which assumes a uniform level of risk among all airline travellers, to one that focuses more intently on passengers thought to pose elevated security risks. Risk-based passenger screening includes a number of initiatives that fit within a broader framework addressing security risks, but specifically emphasizes the detection and management of potential threats posed by passengers. This book examines changes to the Secure Flight program since 2009; TSA's efforts to ensure that Secure Flight's screening determinations for passengers are implemented at airport checkpoints; and the extent to which program performance measures assess progress toward goals.