The United States is now requiring visitors from 35 countries to register online with the U.S. Department of Homeland Security before they can travel into the United States. Here is a list of the countries:

Andorra, Australia, Austria, Belgium, Brunei, Czech Republic, Denmark, Estonia, Finland, France, Germany, Hungary, Iceland, Ireland, Italy, Japan, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Monaco, the Netherlands, New Zealand, Norway, Portugal, Republic of Korea, San Marino, Singapore, Slovak Republic, Slovenia, Spain, Sweden, Switzerland, and the United Kingdom.

So if you are from any of these 35 countries you need to register online for an Electronic System of Travel Authorization before boarding a plane to the U.S.

You can read more here.

How far in advance should they register before they travel?

In most cases, you will receive a status on your application immediately. But it is usually better to register atleast 72 hours before your flight as some application takes up to 72 hours to get an answer.

If your application is denied for whatever reason you might still be eligible to visit with a visa as this only prohibits you from traveling under the Visa Waiver Program.

Good to know... I'll remind my overseas friends before they visit.

Just traveler from the 35 countries need to register online.

When did they start this?

It started January 12, 2009.

Oh wait, I didn't read it properly, it says traveling into the US, I live here, so I guess thats why I never heard about it...

Yea must people living in the U.S. would not have known this.

I wonder if it covers us in any way.