Travellers entering the United States via the Visa Waiver Program (VWP) must apply for Electronic System for Travel Authorization (ESTA) approval no later than 72 hours before departure to the United States.
Real-time approvals will no longer be available. Arrival at the airport without a pre-approved ESTA is likely to cause boarding to be denied. ESTA applies to international travellers entering the US under the VWP, which provides visa-free entry for business travellers and visitors from 38 countries.
For more information, please visit https://esta.cbp.dhs.gov/esta/.