The admission of an alien into the United States as a nonimmigrant shall be for such time and under such conditions as may be prescribed by law and regulations pertinent to the classification or category of visa under which the alien is admitted. The time limits for initial stay, extension of stay, and total stay, depend primarily on the nonimmigrant visa classification.

An alien must maintain the visa status and comply with the conditions of such visa unless lawfully changed to another status. Accordingly, the category of visa held by an alien usually indicates the time limits for stay and activities permitted while lawfully in the United States .