Since its inception in November 2001, the Transportation Security Administration (TSA) has focused much of its efforts on aviation security, and has developed and implemented a variety of programs and procedures to secure the commercial aviation system. TSA funding for aviation security has totaled about $26 billion since fiscal year 2004. This testimony focuses on TSA's efforts to secure the commercial aviation system through passenger screening, strengthening air cargo security, and watch-list matching programs, as well as challenges that remain. It also addresses crosscutting issues that have impeded TSA's efforts in strengthening security. This testimony is based on GAO reports and testimonies issued from February 2004 through July 2008 including selected updates obtained from TSA officials in June and July 2008.