566,706 immediate family members of citizens received green cards in 2016. This includes spouses and children (minors). There is no limit on these applications. A further 238,087 more distantly related family (parents, siblings, aunties, cousins, etc) received green cards through a lottery system/line, but this number is capped.
Together, those family members make up the majority of people who receive permission for permanant residence in the United States. The system was designed to favor "family reunification," to keep families together, and permit them to settle in the United States. Because one family member often is often followed by another, and then another, this system is known as "chain migration."