This may not be for all but only for people travelling to the USA soon. The fee for ESTA will be increasing to US$40, from the current US$21 on September 30, so if you are planning, you may want to apply before this date and save a few dollars.
Source: https://edition.cnn.com/2025/09/06/travel/travel-news-us-vis…
The Visa Waiver Program allows citizens of participating countries to travel to the U.S. for tourism or business for up to 90 days without a visa. The total cost is $21. When you apply, you will pay a $4 processing fee. If you are approved to travel to the U.S., you must pay an additional $17 authorization fee.
Each approved ESTA application is generally valid for two years and allows multiple visits to the U.S. within that period without having to apply for another travel approval. If your passport expires in less than two years, you will receive an ESTA approval valid until the passport's expiration date. When you travel to the U.S. for tourism or business under the VWP, you may stay up to 90 days per visit.


Be careful, when you get the email back from them make sure you check whether it has been accepted or not. I know this sounds obvious but it wasn't very clear and because I had been to Iran mine got rejected. Yeah I'm a bit vague and I should have looked harder! I just assumed it was a given.
unfortunately I did it about three days before my trip. Fortunately the staff at the American embassy were just absolutely unbelievably helpful and managed to fast track the Visa.
This was quite a few years ago and I believe things are a tad stricter now