Consular Processing for US Immigrant Visas
Summary: One of the ways a person may become a permanent resident in the USA, is when he or she entered the USA with an immigrant visa that was issued to him or her at a US consulate overseas. The process of receiving such an immigrant visa is referred to as "consular processing." Consular processing is being supervised by the Department of State, and is subject to rules contained in the Foreign Affairs Manual published by the Department of State of "FAM".
The consular process starts with an immigrant petition (such as I-130 alien relative petition or I-140 petition for alien worker) being filed with USCIS in the United States. Of course, an investor's petition, as well as I-360 self-petition may be good reasons for immigrant visas as well. Once an immigrant petition is approved, it would be transferred in most cases to the National Visa Center or NVC that acts as a "middle man" between USCIS, a beneficiary, and a consulate overseas.
What documents NVC requires a petition visa beneficiaries to submit, what determines a post or location for the Immigrant visa interview, and when a visa registration can be terminated is discussed in detail in detail by our New York Immigration lawyer in here, in her article Consular Process.