One of the easiest ways to immigrate to the U.S. is through family based immigration. Legal residents and U.S. citizens can both sponsor their family members for green cards.
U.S. citizens can get green cards for their parents, children, husbands, wives, brother and sisters. Green card holders cannot sponsor all these relatives, they can only help their husbands, wives and children to get green cards. Relatives of citizens and permanent residents do not belong to the same category. They are grouped into different categories.
Immediate relatives of U.S. citizens are their parents, children, husbands and wives. These relatives have special immigration priority. People who fit into this category need not wait for a long time to immigrate to the U.S. USCIS makes available unlimited number of visas for the immediate relatives. They need not wait for visa numbers to become available. However, to qualify, the children of U.S. citizens need to be below age 21 and unmarried. Likewise, only U.S. citizens above age 21 can sponsor their parents.
Family Preference categories:
U.S. citizens can sponsor their relatives who do not belong to the immediate relatives category under the certain family preference categories. Relatives of green card holders also belong to the family preference categories.
First Preference: Unmarried children, above the age of 21, of U.S. citizens belong to this family preference category. Only the minor children of U.S. citizens fit into the immediate relatives category.
Second Preference A: This category is meant for the spouses and minor children of legal residents. To get green cards under this preference category, children of legal residents must be unmarried and must be below age 21. Green card holders cannot help their parents and their brothers or sisters to get green cards.
Second Preference B: Unmarried children, above the age of 21, of green card holders can get resident cards under this family preference category.
Third Preference: Under this category married children of U.S. citizens and their dependents (their spouses and children below age 21) can get green cards.
Fourth Preference: Brothers and sisters of adult U.S. citizens, their spouses and their minor children, belong to this category.