If you are traveling to or transiting through the United States and you do not need a visa, you must apply for an electronic travel authorization (ESTA) before your trip.
This also applies if you are only passing through the US on your way to another country.
We recommend applying for your ESTA as soon as you have booked your trip. Due to increased security checks, the approval may take time. It is not possible to apply within 72 hours before departure.
You can submit your application through the official ESTA website provided by the US government. Make sure your passport is valid for the full duration of your travel.