This depends on where your passport is from, the specific country you are traveling to and how long you are staying. You can get more information about visa requirements from the nearest embassy or consulate of your destination country.
Americans can easily check if they need a visa requirements at this website:
https://travel.state.gov/content/travel/en/us-visas/visa-information-resources/americans-traveling-abroad.html
For those students who do need to process a visa, don Quijote will be able to provide the required official Letter of Invitation once full payment has been made.