As a general rule, an alien who wants to travel to the United States as a non-immigrant needs a visa. For some non-immigrant visa categories, an alien can obtain the visa directly from the U.S. consulate without having to first apply to and receive approval from the United States Citizenship and Immigration Services (USCIS) (formerly called the Immigration and Naturalization Service (INS)). For other non-immigrant visa categories, an alien has to obtain approval from the USCIS prior to applying for a visa at the U.S. consulate. In those instances, one must be ready to produce evidence of USCIS approval to the U.S. consulate (please click here for information regarding types of visa's that require USCIS approval). Aside from evidence of approval from the USCIS, there are other forms and documents an alien must bring to the U.S. consulate when applying for a visa (please click here) for information regarding the forms and documents needed for a visa application at the U.S. consulate).
The following are categories of non-immigrants seeking entry into the United States who do not need a visa for admission.

1. A Canadian non-immigrant: Canadian citizens and residents who are citizens of a British Commonwealth nation are exempt from the visa requirement for purposes of tourism, limited business activity, and work activity under certain provisions of NAFTA which is a treaty between the U.S. and Canada. (For information regarding TN status, please click here).
2. Visa waiver pilot program: This is a special program allowing non-immigrants from designated countries to enter the United States for purposes of tourism and short-term business. (Please click here for information regarding qualifications for the visa waiver pilot program).
3. Visit of an alien to Canada or Mexico who are in a valid legal status in the U.S.: A visa is not needed for entry into the United States from Canada or Mexico if:

1. The alien has a valid non-immigrant legal status in the U.S. such as B-1, F-1, or H-1 before leaving the U.S. and going to Canada or Mexico.
2. The alien left the U.S., for Canada or Mexico, and came back to the U.S. within thirty days.
   Note: In actuality, this is not an exception to the visa requirement but is considered an extension of the alien's expired visa. (Please click here for more information regarding third country visas).

For more information on non-immigrant visa, please click on the following links:
What is a non-immigrant visa?
Who needs a non-immigrant visa?
What are some common non-immigrant visas?
What is the difference between visa and non-immigrant status?
Consulate process for non-immigrants
Entry into the United States
Visa Waiver Pilot Program (VWPP)
Attorney Fees