U.S. citizens and lawful permanent residents (green card holders) who want to bring close family members to the U.S. permanently. U.S. citizens can petition for spouses, children, parents, and siblings. Green card holders can petition for spouses and unmarried children.
The process typically involves two steps: filing a petition (Form I-130) to establish the family relationship, then applying for the green card itself (Form I-485 if already in the U.S., or consular processing if abroad).
Wait times vary enormously — from months to many years — depending on the relationship and the applicant's country of birth. A lawyer can help you understand where you are in the line.