The nonimmigrant visa classification covers a broad range of visas used to enter the U.S. for work, pleasure or study. Some visas are considered 'dual intent'; you may attempt to obtain permanent residency (a green card) while under that classification. Most nonimmigrant visas, however, require you establish the demonstration of nonimmigrant intent. This means you should demonstrate that you have a permanent residence in your home country that you have no intention of abandoning. The duration of time you may spend in the U.S. can range from a few days to several years, depending on the visa. In most situations, your spouse and unmarried children under the age of 21 may accompany you on a derivative visa.