Current U.S. immigration law allows people who have skills and talents needed in the U.S. to be admitted to the U.S. to work on a temporary or permanent basis. There are more than 20 different kinds of nonimmigrant visa categories and each is identified by an alphabetical designation. Each visa is defined by Congress in the immigration statute to serve a particular purpose, e.g., study, work, diplomatic need, etc. Several of these visas can be used for employment in the United States, under specified conditions. Common characteristics of such visas are:

• The period of admission to the U.S. is for a temporary, specifically defined period of time. In most cases, the individual must maintain an intent to return to his or her home country at the end of the visa period.However, H-1Bs and L-1s are excluded from this rule.
  
  
• Nonimmigrants with permission to work in the U.S.are either sponsored by a U.S. employer based on a specific job offer, and must work only for that employer, or receive work permission for specific objectives. For example, H-1Bs are generally employer specific, while F-1 students granted optional practical training are allowed to work for any employer in their field of study.
  
  
• Most foreign nationals undergo at least two screening processes in order to come to the U.S. First, a Consular Officer at a U.S. Consulate generally decides whether the eligibility factors of a particular visa category are met and whether the person satisfies all other criteria for admission to the U.S. (i.e., is not a criminal, has not previously committed immigration fraud, etc.) before issuing a visa that will allow the individual to come to the U.S. Second, upon arrival, all nonimmigrants are inspected by a U.S. Customs & Border Protection (CBP) officer who reconfirms his/her qualification for admission, determines the appropriate nonimmigrant classification, and authorizes a specific length of stay.
  
  
• Any employer-sponsored nonimmigrants (including H-1Bs and certain L-1s) must have the U.S. Citizenship & Immigration Services (USCIS) approve a petition on their behalf based on defined criteria before the applicant may seek a visa overseas for admission to the U.S.

Please note that some work-authorized categories are limited by annual (fiscal year) numerical levels (e.g., H-1B professionals and H-2B temporary or seasonal workers). Thus, they may not be available at all times and careful planning is required.