That depends on whether you are flying domestic or international. Contrary to what is the popular belief, people who don’t have ID are still allowed to fly on domestic flights in the US, so long as they can clear additional security screening.
Adult passengers (18 and over) are required to show a U.S. federal or state-issued photo ID in order to be allowed to go through the checkpoint and onto their flight. (Children are not required to show identification).
Passengers who do not or cannot present an acceptable ID will have to provide information to the Transportation Security Officer performing Travel Document Checking duties in order to verify their identity. Passengers who are cleared through this process may be subject to additional screening. Passengers whose identity cannot be verified by TSA may not be allowed to enter the screening checkpoint or onto an airplane.
Acceptable IDs include:
• U.S. passport
• U.S. passport card
• DHS “Trusted Traveler” cards (NEXUS, SENTRI, FAST)
• U.S. Military ID (active duty or retired military and their dependents, and DOD civilians)
• Permanent Resident Card
• Border Crossing Card
• DHS-designated enhanced driver’s license
• Drivers Licenses or other state photo identity cards issued by Department of Motor Vehicles (or equivalent)
• A Native American Tribal Photo ID
• An airline or airport-issued ID (if issued under a TSA-approved security plan)
• A foreign government-issued passport
• Canadian provincial driver’s license or Indian and Northern Affairs Canada (INAC) card
• Transportation Worker Identification Credential (TWIC)
Non-US/Canadian citizens are not required to carry their passports if they have documents issued by the U.S. government such as Permanent Resident Cards. Those who do not should be carrying their passports while visiting the U.S.