Visas are required for persons from other countries to enter the United States for work. There are two kinds of visas: immigrant and nonimmigrant. An immigrant visa is a visa issued to persons wishing to live permanently in the United States. Immigration law provides for a yearly allocation of 140,000 employment-based immigrant visas. Nonimmigrant visas are for international travelers (citizens of other countries) coming to the United States temporarily. These visas allow travel to a U.S. port of entry (airport, for example) to request permission of the Department of Homeland Security immigration inspector to enter the United States. A visa does not guarantee entry into the United States. The type of visa needed is defined by immigration law and relates to the principal purpose of the person's travel. While in the United States, temporary visitors are restricted to the activity or reason for which their nonimmigrant visa was issued, with few exceptions. The most important employment-related nonimmigrant visas are the H-1B visas, which are issued to individuals who work in specialty areas of expertise (usually highly technical and professional workers such as computer scientists or engineers). Generally, a bachelor's degree is required to obtain this visa.