All categories of family preference immigrant visas and employment-based immigrant visas are issued in the chronological order in which the petitions were filed until the annual numerical limit for the category is reached.
The filing date of a petition becomes the applicant’s priority date. Immigrant visas cannot be issued until an applicant’s priority date is reached. In certain heavily oversubscribed categories, there may be a waiting period of several years before a priority date is reached.
Check the Visa Bulletin for the latest priority dates.
Further information about visa availabilities and priority dates is to be found at the USCIS website.