Beginning January 12, 2009, all nationals and citizens of Visa Waiver Program countries, including Australia, will need authorization to travel to the United States prior to boarding a U.S.-bound airplane or cruise ship. This authorization may be obtained online through the Electronic System for Travel Authorization (ESTA) ( link as below )

Please ensure all passengers travelling to the US on or after the 12 January 09 have completed this authorisation. This authorisation can be obtained from the US Govt website...https://esta.cbp.dhs.gov/.