ESTA (Electronic System for Travel Authorization) Is an automated system that determines the suitability of citizens of the countries belonging to the Visa Waiver Program (currently 39 countries) to be able to travel to one of the 50 States of the United States without requesting any traditional visa, but with the only issue of the electronic visa ESTA.
The electronic authorization is valid for two years from the date of issue and is obbligatory for all travelers who intend to travel to United States for reasons such as business, tourism or transit to access to other destinations.
Countries participating in Visa Waiver Program.Countries currently participating in VWP are: Andorra, Australia, Austria, Belgium, Brunei, Chile, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Japan , Latvia, Liechtenstein, Lithuania, Luxembourg, Munich, Netherlands, Poland, New Zealand, Norway, Portugal, Malta Republic, San Marino, Singapore, Slovakia, Slovenia, South Korea, Spain, Sweden, Switzerland, Taiwan and United Kingdom.
The request must be submitted online. The authorization need to be obtained at least 72 hours before the beginning of the trip.. However we suggest you to get the ESTA as soon as possible, since any refusal will make you need to apply for a non-immigrant Visa, that will take the relative time.