Visitors from certain countries and adjacent islands can enter the US for short visits without a visa, through the Visa Waiver Program. If your country is on the list, you may visit the US for 90 days or less for business or pleasure. To enter, you must present a machine-readable passport that is valid for six months past your expected stay in the US, and a return ticket for travel to a non-US destination. Upon entry, an immigration inspector will provide you with form I-94W (or you may get one on the plane), which records the duration of your stay. This must be kept with your passport during your visit. Short trips to Canada, Mexico or surrounding islands are permissible, as long as you return within your visa duration period and prove you continue to be eligible.

The hitch in this clearly convenient visa process is two fold. First, if your application is denied for any reason, there is no right to appeal (unless you are applying under the Convention Against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment). Second, if you decide to stay in the US, you cannot change or extend this visa. You will have to leave the country to begin the process.