Security measures for commercial flights have undergone significant changes over time. Boarding a flight from a US airport now requires a boarding pass and security screening controlled by the federal government. Travelers must also be mindful of the contents of their carry-on bags.

This was not always the case, as security checkpoints were previously staffed by private contractors and had more lenient rules. The current security system was developed in response to various attacks and attempted attacks that exposed vulnerabilities.

Further details are available on how these changes came about and the events that led to the implementation of stricter security measures.