In 1999, California enacted legislation allowing same-sex couples to register with the State as domestic partners. Although the new legal status initially entailed few legal rights or obligations, incremental 2001 legislation granted some significant legal rights of marriage to registered domestic partners. In 2003, the legislature acted again, extending almost all the state law incidents of marriage to registered domestic partners. This Article places the 2003 legislation in national and international context. In the United States, California domestic partnership is uniquely legislative in origin. This Article explores the ramifications of its purely legislative genesis. Acknowledging that California domestic partnership represents an important civil rights advance for same-sex couples, the Article argues that it is not sufficient as family law. Although lesbians and gay men have enthusiastically welcomed the recognition and dignity that the legislation confers, only a small minority of same-sex couples have registered in California or in other jurisdictions offering similar opportunities. The Article attributes the low registration rates to causes that are largely extrinsic to the essential character of same-sex relationships. Consequently, the Article suggests, same-sex couples would be better served by a regime that recognizes both registered cohabitation and stable unregistered cohabitation. It notes that many other countries have followed such a two-track approach to opposite-sex and same-sex cohabitation and suggests strategies for moving American law in that direction. Finally, the Article speculates about the social effects of legally recognizing same-sex relationships.