The meanings and purposes of marriage are ever-changing. The history of marriage features a shift from marriage as a property relationship to marriage as a consensual expression of mutual love. Over the past two centuries, the gender hierarchy that once characterized marriage, in both cultural and legal terms, has largely given way to a new model of equality and negotiated roles in the United States and other Western societies. The role of sexual expression within marriage has also evolved, from a focus on its procreative function to recognition of the value of sexual pleasure in its own right. And most of the social and legal constraints on the choice of a marriage partner have fallen away, including restrictions based on class, religion and, most notably, race (Cott 2000). For some, same-sex marriage appears as the next logical and inevitable step in the continuing change and evolution of the institution of marriage. For others, it represents a dangerous undermining of marriage's basic meanings and functions. Marriage today is contested terrain.