Foreign nationals that want to visit the United States must obtain a visa from one of the U.S. Consulates unless they come from one of the visa-exempt countries or Visa Waiver Program countries. The same rule is valid for Puerto Rico and the U.S. Virgin Islands, which are U.S. territories.
U.S. Visas were granted to 8.9 million foreigners visiting America and to 482,000 immigrants in 2012.
A Visa must be obtained unless an individual is
a citizen of a Visa Waiver Program country;
a citizen of Canada, the Republic of the Marshall Islands, the Federated States of Micronesia, or the Republic of Palau;
a British Overseas Territories Citizen from Bermuda or the Cayman Islands;
a citizen of the Bahamas;
a U.S. lawful permanent resident (Green Card holder).
There are different rules for Mexican citizens.
There are about 185 different types of U.S. visas, divided in two main categories:
Nonimmigrant visa – for visits of limited duration, such as business, employment or studies.
Immigrant visa – to permanently move to the U.S. At the port of entry, an immigrant visa holder is inspected and processed for a green card. Upon approval (admission stamp by a CBP officer) a stamp is placed on the foreign passport and it prove permanent resident status for 1 year.
In order to move permanently to the U.S., a foreign national must either have an immigrant visa or a dual intent visa, which is one that allows an immigrant to pursue permanent resident status while in possession of a temporary Visa. The H-1B Visa is the most common non-immigrant Visa allowing dual intent.
Coming to the U.S. on a work visa generally involves a 3-step process. First, the U.S. employer files a petition with USCIS requesting the Visa the best suit the foreign worker. If the employer’s petition is approved, it only authorizes the foreign worker to apply for a visa; the approved approval notice (Form I-797) is not an actual visa. The worker then applies for a visa at a U.S. consulate abroad, and is usually interviewed in his native country. If the U.S. consulate approves the visa, the foreign national is then allowed to come to America. At the U.S. border, airport, or other point of entry into the country, the foreign worker is inspected by an immigration officer of the U.S. CBP office.