The Transportation Security Administration (TSA) is an agency of the United States Department of Homeland Security (DHS) that has authority over the security of transportation systems within, and connecting to the United States. It was created as a response to the September 11 attacks to improve airport security procedures and consolidate air travel security under a dedicated federal administrative law enforcement agency.

The TSA develops broad policies to protect the U.S. transportation system, including highways, railroads, buses, mass transit systems, ports, pipelines, and intermodal freight facilities. It fulfills this mission in conjunction with other federal agencies and state partners. However, the TSA's primary focus is on airport security and the prevention of aircraft hijacking. It is responsible for screening passengers and baggage at more than 450 U.S. airports, employing screening officers in airports, armed Federal Air Marshals on planes, mobile teams of dog handlers, and explosives specialists.

Previously part of the Department of Transportation, the TSA became part of DHS in March 2003. It is currently led by Administrator David Pekoske and is headquartered in Springfield, Virginia. As of the fiscal year 2020, the TSA operated on a budget of approximately $7.68 billion and employed over 47,000 Transportation Security Officers, Behavior Detection Officers, Transportation Security Specialists, Federal Air Marshals, and other security personnel.

The TSA has screening processes and regulations related to passengers and carry-on luggage, including identification requirements, pat-downs, full-body scanners, electronic device restrictions, and explosives screening. The agency has faced criticism and controversy throughout its history for the effectiveness of said procedures, as well as baggage theft, data security, and allegations of prejudicial treatment towards certain ethnic groups.