Anyone travelling to the US on the Visa Waiver scheme will now have to get pre-approved online before they can board a plane.
From Wednesday you will need to get the go-ahead from the Electronic System for Travel Authorization. ESTA approval should only take a few minutes but it is recommended that you apply at least 72 hours in advance of flying, or when you book your flight.
The system has been running since January last year but is compulsory from this week. In June US Customs said over eight million people had used ESTA since August 2008.
ESTA will eventually mean an end to those green forms which ask you if you're a Nazi. But for now you will have to fill the form in too - until the systems get joined up.
You can get yours here.
The European Union has criticised the change as effectively a move to visas. This will become more of an issue should the US follow through with threats to charge for the process. ®