In a September 2008 post, I had blogged about the upcoming Electronic System for Travel Authorization (ESTA), which will go into effect on 12 Jan 2009.
As of now, visitors to the U.S.A. are able to enter the country without a visa. As of 12 Jan 09, entry into the United States will only be possible with this electronic travel authorization.
Passengers need to apply at least 72 hours in advance through the internet at esta application. The authorization will also be granted through the internet. Applications are available in English as well as in German. It is advisable to carry a printout of the authorization on you at time of travel.
In case your travel authorization application gets rejected, you will not be able to board the flight and you need to apply for a visa at a U.S. consulate.
This procedure is mandatory for all passengers entering the United States via air or sea port (this also applies to transit stopovers).
Travelers, entering the U.S. by way of land from Canada or Mexico, are exempt from this rule.