To reduce the separation immediate family members of US citizens may experience while waiting abroad for an immigrant visa, the then Immigration and Naturalization Service introduced the K-3 non-immigrant (temporary) visa. K3 visas are specifically issued to spouses of a US citizens abroad pending the processing of an immigrant visa.
This visa status allows the foreign national spouse to enter the United States as a non-immigrant, unite with the American spouse in the US and then adjust status to permanent residence immigrant whilst in the United States.
The K-3 visa classification, itself, does not confer immigrant green card (permanent residence) status and is not similar to the green card lottery process. To obtain immigrant status, the K-3 non-immigrant must file the form I-485 (Application for adjustment to permanent residence).
Children under 21 years of age may apply for derivative visas known as K-4 visas.
The K-3 petition and visa application is not mandatory. A petition and application for immigrant status may be filed without an additional K-3 process. However, the K-3 visa status is designed for the more expeditious entry of the foreign spouse into the US in the interest of family unification.
K-3/4 non-immigrants may apply for authorization to work in the USA whilst awaiting their immigrant status.