What you can and can't do with it
An approved ESTA is not a visa. It lets you board a U.S.-bound airplane or vessel or present yourself at a land border under the Visa Waiver Program, but it does not determine whether you are admissible to the United States. CBP officers determine admissibility when you arrive.[2],[5]
The Visa Waiver Program permits citizens of participating countries to travel to the United States for business or tourism for stays of up to 90 days without a visa. If you have a valid visa, you can still travel on that visa for the purpose for which it was issued.[3],[5]
Your I-94 record shows your admission status. You can check it on the I-94 website by clicking the 'View Compliance' tab. CBP also sends e-mail reminders about the time left in the United States and notifications to travelers who may have overstayed.[4]
If you received an electronic I-94 on arrival by air, sea or land and depart via land, your departure may not be recorded accurately. A departure will be recorded if you depart via land and re-enter the United States before the expiration date stamped in your passport.[1]