Making a transit in the USA is only allowed if you possess an ESTA , a visa or an American passport. You are already checked for these permits when you check in for your flight to the USA, based on your passport number.
ESTA: easier than a visa
An ESTA is easier to apply for than a visa. For a visa application, an appointment needs to be made at the U.S. Embassy. The costs for a visa are also higher. In contrast, the application procedure for an ESTA happens quickly and easily online. This makes an ESTA the most obvious choice for a transit in the USA.Apply for your transit ESTA now
An ESTA is valid for multiple transfers
The validity of an ESTA is two years unless the passport with which it was applied for expires before that. This makes it possible to use the same ESTA multiple times for a transfer in the USA. You only need to fill in a single date of arrival on the application form. Regardless, it is not necessary and indeed not even possible to provide additional or changed dates of arrival. Only after the ESTA or the passport to which the ESTA is linked expires, does a new application need to be submitted again, if you plan to travel to the USA for a transit or a different travel purpose.
Many travellers journeying from Europe to the American continent make a transfer in the USA
A transfer ESTA is also valid for other travel purposes
In the application form, you are asked if you are only travelling to the USA for a transfer. If you answer in the affirmative, you will not need to fill in a place of stay in the USA. However, if approved, you will still receive the exact same travel authorisation as if you filled in that you are in fact staying in the USA. This means that even with an ESTA that was specifically applied for to make a transfer, you can still stay in the United States of America for 90 consecutive days for a holiday or business trip. Each trip does need to meet the requirements set to usage of an ESTA.
Can I leave the airport during my transfer?
Based on the above, it can be concluded that it is also permitted to leave the airport during the transfer in the USA. The ESTA is after all valid for a stay of up to 90 days. However, keep in mind that your airline and the airport where you will be making the transfer can set limitations. If you want to be absolutely sure you can leave the airport during the transfer, you would do well to check this with the airline.
An ESTA is also required for transit
Sometimes, confusion arises between the terms transfer and transit. With a transfer is meant: you get out of the plane in the USA and proceed with your trip on a different plane. With a transit is meant: you land in the USA, and wait inside or outside the aeroplane before proceeding to your final destination in the same plane. Both for a transfer as well as a transit, an ESTA, visa or U.S. passport is required.