European citizens traveling to the United States for tourism do not need to apply for a visa if the trip does not last longer than 89 days

Instead, they should apply for ESTA - Electronic System for Travel Authorization. ESTA must be applied for online. It costs $21 and is valid for two years

Many European countries are included within the U.S. Visa Waiver Program, which makes it easier for citizens to enter the United States, as it frees them from the need to apply for a visa to enter the U.S. when the trip lasts no longer than 89 days

You apply for ESTA [Electronic System for Travel Authorization] by filling out a mandatory online form that must be completed by all travelers who want to enter the U.S. The cost of applying for ESTA is $21.

ESTA lasts for 2 years or until the passport expires [if the passport expires before the 2-year ESTA validity period]

• Government site for applying for ESTA: https://esta.cbp.dhs.gov/esta/

ESTA can only be applied for by citizens of countries participating in the Visa Waiver Program

Those who hold any U.S. visa [B1; B2; J1; F1; E1; E2; O1 etc.] do not need to apply for ESTA to enter the U.S.

As of December 19, 2016, the ESTA form includes a social media entry: the person must indicate one or more social media profiles that belong to them.

One of the questions included in the ESTA application form asks if you have ever been denied a visa to the United States. If you have ever had your application for a U.S. visa rejected, then you will not be able to obtain ESTA, and in order to visit the United States you will have to apply for a visa after an interview with a U.S. consulate in your country of residence.

The "ESTA" travel authorization is not a visa: it verifies that the person can travel to the United States within the Visa Waiver program and, in essence, functions as an authorization to board a plane or ship bound for the United States without necessarily needing a visa.

If ESTA travel authorization is rejected, it is necessary to apply for a B-1 Business visa for business stays or a B-2 visa for tourist stays

Approved travel authorization does not guarantee the applicant's right to enter the United States. This is true for all issued U.S. visas: the immigration officer on arrival always has the power to deny entry to the United States even if a visa is present.

Countries included in the Visa Waiver Program

1. ITALY
2. Andorra
3. Australia
4. Austria
5. Belgium 
6. Brunei
7. Chile
8. South Korea
9. Denmark
10. Estonia
11. Finland
12. France
13. Germany
14. Japan
15. Great Britain (England, Northern Ireland, Scotland and Wales)
16. Greece
17. Hungary
18. Iceland
19. Ireland
20. Latvia
21. Liechtenstein 
22. Lithuania
23. Luxembourg
24. Malta
25. Monaco
26. New Zealand
27. Norway
28. Netherlands
29. Portugal
30. Czech Republic
31. San Marino
32. Singapore
33. Slovakia
34. Spain
35. Sweden
36. Switzerland
37. Taiwan