Partner Series
What Is a Visa?
Credit: Beto Chagas | Shutterstock.com

More than 60 million travelers enter the United States every year from other countries. Some of these people come to stay for a short time on business or for pleasure, while others wish to reside in the country permanently.

The visa system is designed to keep track of these millions of noncitizens, as well as provide a path to citizenship for those who wish to immigrate to the United States.

There are two main kinds of visas that can be issued to foreigners coming to the United States: immigrant visas and nonimmigrant visas. Immigrant visas, or green cards, are issued to those who wish to obtain permanent resident status.

Nonimmigrant visas — including those given to tourists, international students and temporary workers — are easier to obtain than green cards, and allow travelers to stay in the country for a short period of time.

And although obtaining a visa requires a lot of paperwork and usually includes at least one interview with personnel at a U.S. embassy, the visa itself is simply a sticker or piece of paper placed inside a passport.

The visa specifies a date of issuance and expiration, as well as the number of times a traveler is permitted to enter the United States.

Some travelers are able to extend their visas by filling out the appropriate forms and waivers once they’ve arrived in the United States, but those who overstay their welcome are often denied re-entry into the country.  

Not all foreign citizens need to obtain a visa before visiting the United States. Thirty-seven countries, including most of the European Union, now participate in a visa-waiver program that allows citizens to travel for up to 90 days in the United States without first obtaining a visa.

Follow LiveScience on Twitter @livescience. We're also on Facebook& Google+.