Every month, the Visa Office (VO) establishes Qualifying Dates that determine if a petition will be eligible for processing. Qualifying Dates are the latest priority dates that can be processed for certain visa categories. An immigrant visa petition can only become ready for further processing when the Qualifying Date in the appropriate visa category has advanced up to the priority date of the petition. Petitions may remain at NVC for several months or for many years depending on the visa category and country of birth of the visa applicant.