Nationals of certain countries that have agreements with the United States are permitted to enter the U.S. for business or pleasure without first obtaining a visa. For a discussion on what purposes qualify as business or pleasure, please see B-1/B-2 Tourism and Business Activities. There are currently 36 countries that participate in the Visa Waiver Program.
Even though travelers visiting the U.S. under the Visa Waiver Program do not need a visa, they must still apply for authorization to travel to the U.S. Such an application must be completed and submitted via the Electronic System for Travel Authorization (ESTA) web site.
As a Visa Waiver entrant, you will typically be admitted for 90 days; however, the customs officer who inspects you at the border may admit you for less time. You are not permitted to extend this period or change status for any reason except in the case of emergency. Additionally, you will only be permitted to adjust status to Lawful Permanent Resident if your adjustment is based on marriage to a U.S. citizen or as the child or parent of a U.S. citizen.