The Visa Waiver Program (VWP) enables nationals of certain countries to travel to the United States for tourism or business for stays of 90 days or less without obtaining a visa. VWP eligible travelers may apply for a visa, if they prefer to do so. Not all countries participate in the VWP, and not all travelers from VWP countries are eligible to use the program. Effective Jan. 12, 2009, citizens or nationals from all VWP countries will be required to obtain an approved travel authorization via ESTA to be eligible to travel to the United States under the VWP.

WT/WB Status Upon entry into the U.S., visitors are given either a WT (waiver-tourist) or a WB (waiver- business) status that will be indicated on the I-94 Arrival Departure Record. There are two restrictions on visa waiver status that potential users should be aware of:

The 90-day stay in the U.S. cannot, in any circumstances, be extended. It is never possible to change from the visa waiver status to any other non-immigrant status without departing from the U.S. However, in some circumstances, an individual may adjust status to that of a permanent resident via Family Based immigrant petitions.

Which countries participate in the Visa Waiver Program (VWP)? Participating countries are subject to change, so it's best to check with the U.S. Department of State for the most current information http://travel.state.gov/content/visas/en/visit/visa-waiver-program.html.