If you are a permanent resident, carry your green card (or a copy) with you when you travel. If you are an undocumented immigrant, be careful when you travel. Do not drive unless you have a valid driver’s license.
If you take a plane, bus, or train, you will probably have to show a valid government-issued ID, such as a driver’s license, passport, or employment authorization card. You can travel as a passenger in a car without ID.
You should also be aware of immigration checkpoints, especially near the U.S.-Mexico border.