United States Visas were issued to 6.6 million foreign nationals visiting the United States and to 470 thousand immigrants in 2008.

A foreign national wishing to enter the U.S. must obtain a visa:

• 1) If he or she is not a citizen of one of the thirty-six Visa Waiver Program countries
• 2) If he or she is not a citizen of Canada or Bermuda
• 3) Or if he or she has a statutory ineligibility for visa-free travel (e.g. criminal records)

There are separate requirements for Mexican citizens.

There are two basic types of U.S. visas:

• Nonimmigrant visa - for temporary visits such as for tourism, business, work or studying.
• Immigrant visa - for people wanting to be permanent residents in the United States without any time limitation.

In order to immigrate, one should either have an immigrant visa, or have a dual intent visa, which is one that is compatible with making a concurrent application for permanent resident status (Green Card), or having an intention to apply for permanent residence.

Contrary to a popular misconception, a U.S. visa does not authorize the alien's entry to the United States, nor does it authorize the alien's stay in the U.S. in a particular status. A U.S. visa only serves as a preliminary permission given to the alien to travel to the United States and to seek admission to the United States at a designated port of entry. The final admission to the United States in a particular status and for a particular period of time is made at the port of entry by a U.S. immigration officer. For aliens entering the U.S. in a nonimmigrant visa status these details are recorded by the immigration officer on the alien's Form I-94 (Form I-94W for citizens of the Visa Waiver Program countries entering the U.S. for short visits), which serves as the official document authorizing the alien's stay in the United States in a particular non-immigrant visa status and for a particular period of time.