Quote Originally Posted by Win2Win View Post
No, but you need to fill out the ESTA form after you have booked. Failure to do so can result in refusal of entry.
This.

An ESTA is valid for 2 years and is basically a pre-approved Visa Waiver. Previously European passport holders had to complete a Visa Waiver form and submit it on arrival in the US.

The 2 year limit is a pain as you need to remember when your last ESTA started (there is no paperwork unless you print out the app confirmation and fold it/keep it safe with your passport). Mine was last renewed in July 2013 ... perhaps I should get organised and put a note in my calendar.