Explosives represent a continuing threat to aviation security. The Transportation Security Administration (TSA), within the Department of Homeland Security (DHS), seeks to ensure through the Electronic Baggage Screening Program (EBSP) that checked-baggage-screening technology is capable of detecting explosives. Generally, the explosives detection system (EDS) is used in conjunction with explosives trace detection (ETD) machines to identify and resolve threats in checked baggage. As requested, GAO assessed the extent to which: (1) TSA revised explosives detection requirements and deployed technology to meet those requirements, and (2) TSA's approach to the current EDS acquisition meets best practices for schedules and cost estimates and includes plans for potential upgrades of deployed EDSs. GAO analyzed EDS requirements, compared the EDS acquisition schedule against GAO best practices, and interviewed DHS officials. This is a public version of a sensitive report that GAO issued in May 2011.GAO recommends that TSA, among other things, develop a plan to ensure that new machines, as well as those machines currently deployed in airports, will be operated at the levels in established requirements, collect explosives data before initiating new procurements, and develop a reliable schedule for the EBSP. DHS concurred with all of GAO's recommendations and has initiated actions to implement them.