U.S. Immigration law defines the type of visa you must obtain before attempting to enter the U.S. The type of visa often relates to the purpose of your intended travel.
Most foreign nationals, require a non-immigrant visa to enter to the United States. There are multiple types of non-immigrant visas one can obtain to enter the U.S. The visa must be valid and unexpired at the time of making an entry to the U.S. For example: An individual coming to the U.S. for pleasure would require a visitor visa (also known as a B-2 visa). This type of visa generally allows the individual to enter the United States for a temporary stay.
In the case where a foreign national is seeking to permanently residence in the U.S., he or she must obtain an immigrant visa. This type of visa is generally obtained through a family sponsorship, employment sponsorship, investment or even visa lottery.
In addition, under the visa waiver program, nationals of countries designated by the U.S. State Department are allowed to enter the U.S. by simply being in possession of their valid unexpired passport. These individuals are generally allowed to remain in the U.S. for 90 days.