Many people obtain permanent residence through family members. U.S. Citizens and permanent residents are both eligible to petition for certain family members.
US citizens can file for the following categories of family members
Children under the age of 21
Step children under 21 if the step parent relationship was created before the child’s 18th birthday
Family preference categories
Unmarried sons and daughters (over 21) F-1)
Married children (any age) (F-3)
Brothers and sisters (F-4)
There is a limit on the number of preference category applications that can be filed in any year. There are substantial waits for visas in many categories.
Green card holders can petition for the following relatives under the preference categories.
Children under 21 (F-2A)
Unmarried sons and daughters over 21 (F-2B)
Other family categories
Battered spouse (VAWA)
Fiancée visa (K-1)
V non immigrant
Widow of US citizen
Person born in the US to a diplomat