The Immediate Relatives of a U.S. Citizen and the Immigration Preferences
Parents of U.S. citizens are eligible to apply for permanent resident status as immediate relatives, but only if the U.S. citizen is 21 years older. One thing to point out is that the father-in-law and mother-in-law of a U.S. citizen are not "parents" of the U.S. citizen for immigration purposes. The "immediate relatives" of a U.S. citizen, including parents, spouses, widows, and children of a U.S. Citizen (children who are unmarried and under 21 years of age), can immigrate to the United States without being subject to any visa numerical restrictions.
Immediate relatives may immigrate to the United States on a family based petition. This is the most attractive category, since there is no limitation to the number of immigrants who may qualify under this category and, in most cases, visa numbers are immediately available for these individuals to apply for lawful permanent residence.
Immediate relatives include spouses, children and parents of U.S. citizens. Immediate relatives of a U.S. citizen can immigrate to the United States without being subject to any numerical restrictions. This means there is no visa quota allowed under the immediate relative category, unlike other close family members of U.S. citizens or permanent residents. The immediate relatives of a U.S. citizen can apply for U.S. permanent resident status without any waiting time.
The rest of the relatives are divided into several groups called "preferences." Each preference is given a numerical quota per year to limit the number of immigrants admitted into the United States. The four preferences are as follows:
1st Preference: applies to unmarried sons and daughters of U.S. citizens;
2nd Preference: applies to spouses and unmarried sons and daughters of lawful permanent residents;
3rd Preference: applies to married sons and daughters of U.S. citizens;
4th Preference: siblings of U.S. citizens.