The USA ESTA is a mandatory requirement for visa-exempt visitors and is applicable to certain nationalities. Eligible travelers can register online through the Electronic System for Travel Authorization (ESTA) for trips to the United States for tourism, transit, and business purposes. The ESTA authorization is valid for 2 years from the date of issue and allows multiple entries, with a maximum stay of 90 days each time. The ESTA application process is simple and requires personal and passport information, as well as a few questions related to security and health. It is recommended to apply for ESTA at the time of booking travel, but not less than 72 hours before departure, to allow for pre-screening by the US Department of Homeland Security.