Which amendment is frequently cited in arguments for gay marriage?

The 14th Amendment is frequently cited in arguments for gay marriage because it contains crucial clauses that guarantee equal protection under the law and due process rights. Specifically, the Equal Protection Clause mandates that no state shall deny any person within its jurisdiction the equal protection of the laws. This has been interpreted to mean that same-sex couples should have the same legal rights as heterosexual couples, particularly regarding marriage.

Historically, landmark Supreme Court cases, such as Obergefell v. Hodges in 2015, relied on the 14th Amendment when ruling that same-sex marriage is a constitutional right. The decision emphasized that denying same-sex couples the right to marry violates both the Equal Protection and Due Process Clauses of the 14th Amendment, thus framing the argument for marriage equality in terms of civil rights and equal treatment under the law.