The K-1 visa is a non-immigrant visa that allows a foreign national fiancé(e) of a U.S. citizen to enter the United States for the purpose of marriage. The couple must marry within 90 days of the fiancé(e)'s arrival in the U.S. to maintain the visa's validity. To obtain a K-1 visa, the U.S. citizen must file a petition with the U.S. Citizenship and Immigration Services (USCIS). After approval, the foreign fiancé(e) can apply for the visa at a U.S. embassy or consulate. This process includes background checks and an interview to ensure eligibility.