Whether it's a quick trip across the state or a daylong journey from Alaska to Florida, boarding a domestic flight doesn't require a passport – but a library card or Costco membership card won't cut it. Adults 18 and over must show photo identification before boarding a domestic flight, while children need an ID only in certain circumstances. The TSA accepts more than a dozen different types of ID for domestic travel.

Acceptable ID for Adults

There's a good chance you're already carrying an acceptable ID for domestic travel in your wallet right now. The TSA accepts standard driver's licenses, enhanced driver's licenses and other DMV-issued state photo identity cards. A valid U.S. passport or passport card is also a suitable form of ID for domestic travel. Members of any of the Department of Homeland Security's trusted traveler programs – Global Entry, NEXUS, SENTRI and FAST – may show their ID cards.

Other acceptable forms of photo ID include permanent resident cards, U.S. Department of Defense IDs, Canadian provincial driver's licenses and federally recognized, tribal-issued photo IDs.

Acceptable ID for Children

The TSA agent stationed at the security checkpoint of your airport probably won't ask to see an ID for a child under the age of 18. Minors aren't required to show any identification for a domestic flight. It's still a good idea to be prepared to show ID, however, for a few reasons.

Airlines allow children under the age of 2 to travel on a parent's lap instead of having their own seat. Gate agents are on the lookout for parents who try to skirt that rule by carrying older children on their laps instead of buying them their own seats, so bring a copy of a child's birth certificate if he's nearing 2 and doesn't have his own ticket. Airline employees may ask for proof of age to make sure the child is truly young enough to travel without a seat.

On the other end of the spectrum, be prepared to prove the age of an older teen. Although the TSA doesn't require ID for minors, a 16- or 17-year-old may look close enough to 18 that an agent will ask for identification. A driver's license or a copy of the teen's birth certificate should be sufficient to prove he's still a minor.

Carrying a copy of a child's birth certificate is also useful in the event that officials raise questions about your right to travel with him. The TSA looks out for kids who are being kidnapped or trafficked and may ask to see proof that both of the child's parents give permission for him to fly. It becomes more of an issue for international flights, but if you're traveling with a child who isn't yours, carry a notarized letter of permission from his parents just in case.

What Happens When You Don't Have Your ID?

Lost your license on vacation? All hope is not lost. The TSA will work with you to try to verify your identity. Expect to be asked to provide some personal information, which agents can compare to public databases and other sources in an attempt to confirm that you are who you say you are.

The TSA doesn't disclose exactly what information you'll be asked to share, but expect to be asked about details that are on your birth certificate, such as your mother's maiden name. This process takes time, so arrive at the airport at least two hours before your flight if you know you've misplaced your ID.