TSA stands for the Transportation Security Administration. It was created in the immediate aftermath of the September 11, 2001, terrorist attacks as part of the Aviation and Transportation Security Act signed by President George W. Bush. Before the TSA, airport security in the United States was largely handled by private security firms hired by the airlines themselves. The creation of the TSA moved this responsibility into the hands of the federal government to ensure a standardized, rigorous level of screening across all 450+ U.S. airports. While most people associate the TSA strictly with airport checkpoints, their mandate actually covers all modes of transportation, including highways, railroads, buses, mass transit systems, pipelines, and ports. Today, the TSA is a component of the Department of Homeland Security (DHS) and employs approximately 50,000 Transportation Security Officers who screen over 2 million passengers and their baggage every single day.