Many people immigrate to the United States every year based on a family petition filed by their spouses, fiancés, parents, children, or siblings. How quickly they can come depends largely on whether they are an "immediate relative" or a family member in one of the four preference categories established by the Immigration and Nationality Act.
Immigration through an Immediate Relative
According to US immigration laws, an "Immediate Relative" is a parent, spouse or child (unmarried and under 21 years of age) of a U.S. citizen. Immediate relatives of a U.S. citizen can immigrate to the United States without being subject to any numerical restrictions, unlike other close family members of U.S. citizens and/or permanent residents. This means they can apply for permanent resident status or an immigrant visa without having to wait in "line". For more about the process, including information about Conditional Permanent Residence, read the following links:
Immigration through Family-Based Preference Categories
Immigration through other close family members (who are not immediate relatives) is a very different experience because unlike immediate relatives of a U.S. citizen, family preference categories are subject to annual numerical limitations that often create a significant backlog delaying the family member's immigration by sometimes years or even decades. Those who wish to petition for their family members must know a number of key facts, including their family member's preference category and whether that particular category is "current" (are visa numbers available for the particular category). This information can be obtained by visiting Department of State's Visa Bulletin, which updates this information on the monthly basis.
Immigration through a same-sex marriage
On June 26, 2013, the United States Supreme Court struck down Section 3 of the Defense of Marriage Act finding that the law's definition of marriage as a union between a man and a woman was unconstitutional. This landmark decision removed a decades old ban on the federal recognition of same-sex marriages allowing same-sex married couples to be recognized by the federal government and receive federal benefits. Consequently, USCIS and US Department of State's Embassies and Consulates adjudicate green card and visa applications based on same-sex marriages in the same way they adjudicate applications for opposite gender spouses.
Family-based preference categories