One method of obtaining lawful permanent residency is through a qualifying relative who is either a United States citizen or a lawful permanent resident. United States citizens and lawful permanent residents can help their qualifying foreign relatives in petitioning for lawful permanent residency in the United States and eventually even citizenship. There are different categories family-based immigration.
                                                                             IMMEDIATE RELATIVES 
An immediate relative can be a spouse of a United States citizen, widow of a United States citizen, unmarried child under the age of 21 of a United States citizen, or a parent of an adult United States citizen. Returning residents are immigrants who previously resided in the United States with lawful permanent resident status and are returning to live in the United States after residing abroad for more than one year.
                                                                           PREFERENCE CATEGORIES 
There are four preference categories for limited family-based immigration. The first preference category consists of unmarried children of United States citizens who are over the age of 21. The second preference is divided into “2A” and “2B”.Spouses of lawful permanent residents as well as their unmarried children under the age of 21 fall into the “2A” category whereas unmarried sons and daughters of lawful permanent residents who are over the age of 21 fall into “2B” category. The third preference consists of married children of United States citizens. The fourth preference category consists of siblings of adult United States citizens.