The non-immigrant visa classification covers a broad range of visas used to enter the United States for work, pleasure or study. Some visas are considered 'dual status'; you may attempt to obtain permanent residency (a green card) while under that classification. Most non-immigrant visas, however, require you establish the demonstration of non-immigrant 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 US 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.