TSA stands for Transportation Security Administration. On September 11, 2001, 3,000 people were killed in terrorist attacks at the World Trade Center in New York, and in Pennsylvania and Virginia. The TSA was designed to prevent similar attacks in the future. It was created as part of the Aviation and Transportation Security Act which was passed by the 107th Congress and signed into law on November 19, 2001. In March 2003, the TSA was transferred to the U.S. Department of Homeland Security. Its mission is to "protect the nation's transportation systems to ensure freedom of movement for people and commerce."