Danish citizens qualify for the Visa Waver program and can therefore travel to the United States without a visa. This means that as a Danish citizen you can apply for an ESTA in the USA. So you don’t need a regular US visa.
The average processing time for an ESTA application is 30 minutes. However, it is recommended that you apply for an ESTA at least 72 hours before departure, as in some cases it can take up to 3 days for an application to be approved.
An ESTA can be used for tourism and business travel. If you need anything other than these purposes in the US, you will need to apply for a US visa.
In some cases, an ESTA application is refused. They cannot find out a reason for the rejection of your application. If your application is rejected, you will have to apply for a visa. A visa process takes about 1 month and you have an interview at the US embassy in Copenhagen.
ESTA is a travel permit and not a visa
There are many misconceptions about what an ESTA really is. An ESTA is an electronic travel authorization that you can use to board your flight to the United States. In theory, you could still risk being turned down by immigration at the airport of arrival in the United States.
When you arrive in the US, the border guards will ask you questions about your stay in the US. If they are dissatisfied with your answers or if they suspect you, for example, of wanting to work in the USA or not to leave the USA, you run the risk of being turned away at the border.
If you are refused on arrival at the United States airport, you will be held until you can be put on your next flight to the United States.