When entering the United States by sea or air under the Visa Waiver Program, you are required to apply for your travel permit under Electronic Systems for Travel Authorization (ESTA). It is administered by the Customs, Border Protection, and Department of Home SEcurity.

ESTA visa is used to determine if such travel carries any security or law enforcement threat.

It’s approval permits the traveler to board an air or sea carrier for travel to US under VwP. Note: Private carriers should be a signatory VwP carrier. Whereas CBP advises that you apply for your ESTA 72 hours before your traveling date, you can apply for it any time before boarding your carrier, in majority of cases, the response is going to be received within seconds after you have made your submission.

ESTA is different from a visa. It doesn’t meet the legal requirements of a US visa, in lieu when a visa is required. Travelers who have a valid US visa can travel to US on that visa for that purpose it was issued. And travelers who travel on valid visas aren’t required to apply for ESTA. Similar to the way that your valid visa doesn’t guarantee admission to the US, also an approved ESTA is not going to be a guarantee of admission.

ESTA became a mandatory requirement 12 January 2009. VWP applicants must complete a blue Customs declaration when they arrive in US, whether or not they have an ESTA authorization.

Approved ESTA applications should be valid for for two years, or till the expiry of their passports, or whichever comes first.

When you’re traveling to the US with approved ESTA, you can stay only for up to 90 days, at a time, and there must be some reasonable amount of time between your visits so the CBP Officer doesn’t think you’re trying to live in the country. There’s no set requirements for a period you should wait between visits, though.

Those approved ESTA applicants, but whose passports are going to expire within two years , are going to receive an ESTA that’s valid until their passports expire.

Among other things, a new ESTA authorization will be required if:

You’re issued a new passport

You have a name change-first and/last

You change your country of citizenship

There’s a change in your circumstances, for example you’re convicted of some crime of moral turpitude, or you contract a contagious disease. Note: Such a change might require you to have a visa to travel to the US. You must apply again, and your application should reflect the change in your circumstances, or else you might be denied entry when you try entering United States.