Several nationalities are exempt from US visa requirements under certain conditions. This exception is part of the Visa Waiver Programme (or Visa Waiver Program in English).
Visa Waiver Program and ESTA: definitions
Countries in blue are part of the Visa Waiver Programme (VWP)
ESTA should not be confused with a visa. The ESTA is an authorisation that gives you the right to travel to the USA. Once there, you can benefit from visa exemption and enter the country.
Your airline must be one of the signatories of the Visa Waiver Program. On almost all commercial airlines, you have nothing to worry about. For private flights, the aircraft must belong to an American company or a non-American operator with a subsidiary in the United States.
At the border between the USA and its neighbouring countries (Canada, Mexico), the seizure of the form I-94W will be replaced by the ESTA electronic authorisation from 2 May 2022 !
Reasons for refusal of the Visa Waiver Program
Nationality
You must be a national of one of the VWP member countries listed above. You must have a passport from one of these countries in order to apply for your ESTA electronic travel authorisation.
Length of stay
If you are planning to stay in the USA for more than 90 daysYou will not be able to benefit from visa exemption and will have to apply for a traditional visa.
Purpose of the trip
If you are travelling for a purpose other than tourism, business or transit (such as working on American soil), the visa exemption does not apply to you. To get a job or do an internship in the USA, you will need a specific visa.
Other reasons
Even if you meet the various conditions mentioned above, the US immigration authorities are entitled to refuse you entry to the USA if one or more of the answers given to the ESTA questionnaire contravene the laws in force in that country. In some cases, you can still travel on a conventional visa.