The transformation of American public opinion on same-sex marriage is among the most remarkable and rapid shifts in moral consciousness ever recorded. The case of same-sex marriage, in particular, provides an astonishing example of social progress at scale, propelled by democracy, among a public full of spite and misinformation. In 2015, the push for same-sex marriage culminated with the landmark Obergefell v Hodges Supreme Court decision, which secured the right to same-sex marriage as a matter of US federal law. Remarkably, in spite of the Donald Trump administration’s reactionary push against transgender rights, there has been no widespread movement to walk back same-sex marriage rights. Survey research confirms that the single most important factor in causing people to change their mind about same-sex marriage was personal contact.