One of the ways a foreign national (alien) can become a permanent resident is through a permanent employment opportunity in the United States. There are five employment-based preference categories.
Each month, the Visa Office subdivides the annual preference and foreign state limitations specified by the INA into monthly allotments based on totals of documentarily qualified immigrant visa applicants reported at consular posts and CIS Offices, grouped by foreign state chargeability, preference category, and priority date. If there are sufficient numbers in a particular category to satisfy all reported documentarily qualified demand, the category is considered "Current." For example: If the monthly allocation target is 3,000 and there is only demand for 1,000 applicants, the category wi