To study abroad, you must have a signed, valid passport from your country of citizenship that will not expire for a minimum of 6 months after your planned return date. If you do not have a passport, or it's about to expire, make sure you apply or renew as soon as possible! US Citizens can refer to the US Department of State's website for more information regarding passports.
A student visa is permission by a foreign government to live and study in that country. It typically comes in the form of a stamp that is inserted directly into your passport. All US passport holders must obtain a student visa prior to departure. Thai consulates won't accept student visa applications more than 90 days before departure. However, please apply early within this time period to ensure you receive your visa prior to departure. If you plan on traveling outside of Thailand, you should apply for a multiple entry student visa.
Further information will be posted to your Student Gateway account in the Visa Guide, which you will receive after you have been accepted into your USAC program (typically 3 months prior to departure). Program Advisors in the Central Office are also available to answer any visa questions you may have.
Check with your home country consulate, as well as the embassy of the country in which you plan to study, regarding visa requirements. Permanent Residents of the US should check with US Immigration as leaving the country for more than one year may jeopardize permanent resident status. Tax clearance and re-entry forms may also be necessary in these cases.