The immigration and Nationality Act sets the number of immigrant visas that may be issued to individuals seeking a green card each year.
Immigrant visas available to “immediate relatives” of U.S. citizens are unlimited, so are always available. Immediate relatives include, parents of a U.S. citizen, spouses of a U.S. citizen and, unmarried children under the age of 21 of a U.S. citizen.
Immigrant visa numbers for individuals in a “preference category” are limited, so are not always available.
The U.S. Department of State is the agency that distributes visa numbers. Family sponsored preference categories are limited to a minimum of 226,000 per year and employment based preference visas are limited to a minimum of 140,000 per year. In addition, there are limits to the percentage of visas that can be allotted to each country.
To distribute the visas among all preference categories, the Department of State gives out the visas by providing visa numbers according to the preference category and one’s priority date.
The priority date is used to determine an individual’s place in line in the visa queue. When the priority date becomes current, the individual will be eligible to apply for an immigrant visa.