A K-1 visa is a United States non-immigrant visa that benefits a fiancés and the fiancées of US citizen petitioners.
An ordinary person might not realize it but any K1 visa attorney would know that this form would not be used for the fiancé of a person who is not a citizen of the United States.
The Application concerning spouse immigration is made by the petitioner in the US on a USCIS form I-129F filed by mail at a USCIS Service Center.
The petitioner must provide detailed information and supporting documentation to prove that both parties are legally free to marry, have met each other within the last two years, intend to marry, do not have disqualifying criminal histories (so-called crimes of moral turpitude), and proof of identity and citizenship.
Recent changes to the Law also limit the number of petitions a petitioner can make, and the petitioner must not have a criminal history of sexual or partner abuse.
Other recent changes in the Law also severely limit the role of "marriage agencies" in the introductions, and any involvement of such agencies must be disclosed.
If the spouse is a guest worker he or she may need to apply for a H-1B non-immigrant visa.
Concerning the A K-1 visa.
If approved (eight months is about normal, though this varies based on processing time, and to a degree the relevant embassy), the Application materials will all be forwarded to the National Passport Center for processing.
Then the whole paper file wrapper is sent to the US embassy or consulate in the jurisdiction in which the fiancé(e) resides abroad.
The Embassy will contact the fiancé(e) and schedule an interview date.
In the meantime, the fiancé(e) has to have a medical examination at an approved clinic, to screen for certain infectious diseases like HIV, Tuberculosis and Syphilis.
The Embassy staff will question the fiancé(e) and ask for additional documents, to determine the authenticity of the relationship (amongst other things, that it is not an attempt to skirt 'the proper channels' of US immigration law), though the preliminary questioning in this regard is fairly straightforward and brief.
If the interview goes well, the visa is granted immediately, but the fiancé(e)'s passport may need to be kept for a few days for processing.
The fiancé(e) then has six months to enter the US, and 90 days after that to marry the petitioner.
The fiancé(e) cannot marry any other person, and must return if not married to the petitioner.