What is the difference between immediate relatives and preference relatives in family-based immigration?

Immediate relatives are the closest family members of U.S. citizens (spouses, unmarried children under 21, and parents), and they are not subject to annual visa caps, allowing for quicker processing. Preference relatives include more distant family members of both U.S. citizens and lawful permanent residents (green card holders). Their visas are subject to annual limits, which can lead to long waiting times. The eligible family members are:

For U.S. citizens:

For lawful permanent residents (green card holders):