The K-3 visa is for the foreign spouse of a U.S. citizen. It was designed to shorten the physical separation between the foreign national and his or her U.S. citizen spouse. Specifically, it allows foreign nationals to enter the United States to await approval of the immigrant visa petition. K-3 visa recipients subsequently apply to adjust status to a permanent resident (green card holder) so that he or she may live permanently in the U.S. with their spouse.

However, for most applicants, the K-3 visa isn't worth it. In 2019, U.S. Citizenship and Immigration Services (USCIS) issued only five K-3 visas. Since the K-3 visa processing can take a while, it sometimes takes just as long as it would to directly get your marriage green card.

Suppose you and your spouse are already married with a pending Form I-130. In that case, you should probably directly apply for a green card via consular processing, which takes the same time. Once you arrive in the United States with an approved green card, you can work immediately as a permanent resident without having to file additional applications.