When New York adopted a law to permit same-sex marriage, it sought to eliminate inequality; but DOMA frustrates that objective through a system-wide enactment with no identified connection to any particular area of federal law. DOMA writes inequality into the entire United States Code.
— Excerpt from the majority opinion in United States v. Windsor, authored by Justice Anthony Kennedy and joined by Justices Ruth Bader Ginsburg, Sonia Sotomayor, Elena Kagan and Stephen Breyer.