A K-1 visa is a nonimmigrant visa issued to the fiancé(e) of a United States citizen to enter the United States. A K1 visa requires a foreigner marry his or her US citizen petitioner within 90 days of entry, or leave the US. Once the couple marries, the foreign citizen can adjust status to become a lawful permanent resident of the United States. Although a K-1 visa is legally classified as a non-immigrant visa, it usually leads to important immigration benefits and is therefore often processed by the Immigrant Visa section of United States Embassies and Consulates worldwide.
The unmarried children, under 21 years old, of a K1 visa beneficiary can also immigrate with their parent. Because such children derive their immigration status through a parent, they are known as derivative applicants, and are issued a K2 visa. Derivative children may either immigrate at the same time as their parent, or may follow to join the parent up to one year after the issuance of the parent's K1 visa.
Two additional "K" categories of visas exist. The K3 visa is for the spouse of a US citizen. It was created to allow a foreign spouse of a US citizen the opportunity to immigrate to the US and adjust status to an immigrant visa. It is similar to the IR1/CR1 category which are also for the spouse of a US citizen. The only practical difference is that a K3 visa is a non-immigrant visa, thus the foreign spouse must adjust to immigrant status after arrival in the US. The IR1/CR1 visa categories are immigrant visas thus require no adjustment of status once the beneficiary has arrived in the United States. A K4 visa is a derivative visa issued to the child of a K3 visa holder.
