For non-US citizens, you must have a passport in good condition, valid 6 months after your return. Besides, your passport must have at least two blank pages for entry or exit.
For 36 countries a visa is not required to enter the US territory. However, you must have an electronic travel authorization: Electronic System for Travel Authorization (ESTA). The application must be made at least 72 hours before your arrival and costs $21 USD. Once validated, your registration is valid for 2 years.
We strongly advise you to check the US access conditions with the US consulate in your country.