The U.S. income tax code encourages marriage for some and discourages marriage for others, but same-sex couples were only recently exposed to these incentives. We estimate marriage responses by exploiting variation in the recognition of same-sex marriages for tax purposes versus earlier papers leveraging smaller changes. Using the American Community Survey, which reports cohabitation and marriage, we estimate a significant though very small marriage elasticity, with further analysis suggesting a higher (though still small) elasticity for low-earning households and in response to federal taxes specifically. Our estimates imply that the 2018 tax reform will increase marriage among high-earning cohabiting couples.