The family preference immigrant visas are divided into priority preference and usually granted according to which preference category the family members fall into. A limited number of green cards are available for non-immediate family members of U.S. citizens and immediate relatives of Green Card holders. The categories, in order from the most preferred to the least preferred, are:
First Preference: unmarried sons and daughters who are over the age of 21 of a U.S. citizen and their children under the age of 21
Second Preference: spouses, minor children (under the age of 21), or unmarried sons and daughters over the age of 21 of a U.S citizen or a Lawful Permanent Resident.
Third Preference: married sons and daughters of a U.S. citizen, their spouses and minor children.
Fourth Preference: a brother or sister of a U.S. citizen over the age of 21, their spouses and minor children.