This article analyses some familiar arguments both for, and against, same-sex civil marriage. I argue that it is not enough to defend gay marriage by a simple appeal to equality, unless one addresses the view that same-sex marriage would be contrary to the objective nature and purpose of marriage. I illustrate the ways in which a stand-off is reached in discussions of this particular matter. I also suggest that there is a mystery about what the ‘upgrade’ from a faithful relationship to marriage amounts to, but that part of the answer is that marriage embodies a state-recognized social transition. This is underpinned by the interest that society has in marriage, largely owing to its facilitating a stable environment for children. However, I suggest that marriage also properly functions as a way to uphold commitment and love, and conclude that that there is no good reason not to uphold – through marriage – those things in same-sex relationships. But I concede that religious organisations with theological objections to same-sex marriage should not be obliged to conduct gay weddings.