Temporary Employment Visa Categories

Overview and Types of Visas (Classifications)
The Immigration and Nationality Act provides several categories of nonimmigrant visas for a person who wishes to work temporarily in the United States. If you want to work in the U.S. temporarily, under immigration law, you need a specific visa based on the purpose of your travel and type of work you will be doing.  Some visa classifications are subject to annual numerical limits, referred to as “caps.”  These numbers, if applicable, are shown below in parentheses.

• H-1B classification applies to persons in a “specialty occupation” which requires the theoretical and practical application of a body of highly specialized knowledge requiring completion of a specific course of higher education (65,000);
• H-2A classification applies to temporary or seasonal agricultural workers;
• H-2B classification applies to temporary or seasonal nonagricultural workers. This classification requires a temporary labor certification issued by the Secretary of Labor (66,000);
• H-3 classification applies to trainees other than medical or academic. This classification also applies to practical training in the education of handicapped children (50);
• L classification applies to intra-company transferees who, within the three preceding years, have been employed abroad continuously for one year, and who will be employed by a branch, parent, affiliate, or subsidiary of that same employer in the U.S. in a managerial, executive, or specialized knowledge capacity;
• O-1 classification applies to persons who have extraordinary ability in the sciences, arts, education, business, or athletics, or extraordinary achievements in the motion picture and television field;
• O-2 classification applies to persons accompanying an O-1 alien to assist in an artistic or athletic performance for a specific event or performance;
• P-1 classification applies to individual or team athletes, or members of an entertainment group that are internationally recognized (25,000);
• P-2 classification applies to artists or entertainers who will perform under a reciprocal exchange program;
• P-3 classification applies to artists or entertainers who perform under a program that is culturally unique (same as P-1);
• Q-1 classification applies to participants in an international cultural exchange program for the purpose of providing practical training, employment, and the sharing of the history, culture, and traditions of the alien’s home country; and
• TN classification applies to citizens of Canada or Mexico in specific jobs named in the NAFTA treaty.

Some information courtesy of U.S. Department of State website
Page Summary: There are a number of visa categories under which a foreign worker may obtain temporary work authorization, including the most common categories of H, L, O and TN (if a Canadian or Mexican citizen).