The field of immigration law involves people traveling to the U.S permanently, to live and work or temporarily to work or visit. In order to travel to the U.S. on a permanent basis or temporary basis, you need appropriate permission from the U.S. government. This permission is generally known as visa. A visa is of two types—non-immigrant visa and immigrant visa. The two most instrumental agencies involved in the process of traveling to the U.S. are the U.S. Department of State and the U.S. Citizenship and Immigration Services.