Even in secular contexts, marriage retains sacramental connotations. Yet what is its moral significance? This book examines its morally salient features – promise, commitment, care, and contract – with surprising results. In Part One, “De-Moralizing Marriage,” essays on promise and commitment argue that we cannot promise to love and so wedding vows are (mostly) failed promises, and that marriage may be a poor commitment strategy. The book contends with philosophical defenses of marriage to argue that marriage has no inherent moral significance. Further, privileging marriage sustains amatonormative discrimination – discrimination against non-amorous or non-exclusive caring relationships such as friendships, adult care networks, or polyamorous groups. The discussion raises issues of independent interest for the moral philosopher such as the limits of promising and nature of commitment. The central argument of Part Two, “Democratizing Marriage,” is that liberal reasons for recognizing same-sex marriage also require recognition of polyamorists, polygamists, friends, urban tribes, and adult care networks. Political liberalism requires the disestablishment of monogamous amatonormative marriage. Under public reason, a liberal state must refrain from basing law solely on moral or religious doctrines; but only such doctrines could furnish reason for restricting marriage to male-female couples or romantic dyads. Restrictions on marriage should be minimized. But there is a strong rationale for minimal marriage: social supports for care are a matter of fundamental justice. Part Two responds to challenges posed by property division, polygyny, and parenting, builds on feminist, queer, and anti-racist critiques of marriage, and argues for the compatibility of liberalism and feminism.