The United States Department of Homeland Security requires citizens of qualifying VWP countries to obtain a travel authorisation prior to initiating travel to the United States under the Visa Waiver Program. This authorisation may be obtained online through the Electronic System For Travel Authorization (ESTA). Please note: For applications submitted on or after 8 September 2010, there will be a fee of $14 per applicant.
Customers travelling under the VWP must obtain electronic travel authorisation prior to boarding their flight to the United States. If they do not receive travel authorisation prior to departure they may be denied boarding, experience delays or be denied admission into the United States. Applications can be made online anytime prior to travel, but it is recommended that applications are made no later than 72 hours prior to departure.
ESTA requires submission of data that is currently provided by travellers arriving at US ports of entry on the green I-94W landing card. ESTA is mandatory for all Visa Waiver travellers and over time the old, green I-94W forms will be phased out, however both forms are currently required to be completed until further notice. No more information is being requested under ESTA than is currently required on the I-94W.
Submit an ESTA application: https://esta.cbp.dhs.gov/