USA visas fall under one of two broad categories, immigrant and non-immigrant.
An immigrant visa is required for foreigners who are planning to live permanently in the USA, regardless of whether or not they intend to seek employment. They have to be sponsored by a US based employer or a relative who is a US citizen in order to qualify for an immigrant visa.
The immigration authority usually requires an Affidavit of Support from aliens sponsored by US based relatives or US employers, as proof of financial capacity of either the petitioner or the sponsoring parties. By filing this form, the petitioner or his sponsor is guaranteeing that the immigrant will not be a fiscal burden on the US government. Where the affidavit should be submitted depends on whether the party being sponsored is inside or outside the USA.
A non-immigrant USA visa is required from foreigners who are planning to travel to the country and to stay there for a short period of time. Petitioners may cite reasons such as tourism, medical care, business travel, college education, student exchange programmes, temporary employment, concerts, news coverage and diplomatic or state visits, among others.
The three main types of temporary work visa are H1B, (Specialty Occupation Visa), L1 (Intra-Company Transfer Visa) and E (Treaty Trader or Treaty Investor Visa). The H-1B Visa provides a three-year residency for contractual workers, though the duration may be extended. L1s are aimed at managerial employees who must be relocated to the US branch of their employer, while E visas are intended for investors, be they individuals or corporations.