K1 visas are issued by the US Consulate to the fiancé/fiancée of a United States citizen. It is a temporary visa that requires the foreign fiancé/fiancée to contract marriage with the US citizen within 90 days of entry into the United States. The US citizen is required to file a temporary residence petition (K-1/I-129F petition). On the approval of the petition, the foreign fiancé(e) files an application for a K-1 visa. Once in the United, an adjustment of status to permanent residence should be effected once a marriage has taken place.
In order to obtain temporary migration to the USA by law, the couple must provide evidence that they have physically met within the last two years, unless religious principles prevent them from meeting each other before the wedding. Types of proof that may be submitted for these purposes are relatively flexible and can include letters, emails, phone bills and photographs of the couple together.
Under US immigration law, the US citizen must establish that he is a United States citizen and the couple must prove that they are free to marry.
The K-1 visa ultimately culminates in US migration and green card status once marriage and adjustment of status have been properly effected.