In Perry v. Schwarzenegger, Chief Judge Vaughn Walker held that Proposition 8—an amendment to the California Constitution that prohibits same-sex couples from marrying—violates the Due Process and Equal Protection Clauses of the Fourteenth Amendment. To date, legal experts have claimed that although Judge Walker’s factual findings may be novel and significant, his legal analysis is familiar and not likely to have a significant impact on the future of same-sex marriage law. This Article argues that the common wisdom about Judge Walker’s ruling is misguided, because it overlooks novel aspects of Judge Walker’s legal analysis that have the potential to make valuable contributions to the development of same-sex marriage law, in this case and others. By building upon passages from Judge Walker’s ruling, the Article develops three new challenges to the constitutionality of laws that prohibit same-sex couples from marrying. Part I argues that the historical relationship between discrimination based on sex and discrimination based on sexual orientation can provide a basis for applying heightened scrutiny to laws against same-sex marriage under the Due Process Clause, as an alternative to the prevailing theory that calls for applying heightened scrutiny to such laws under the Equal Protection Clause. Part II argues that the Due Process and Equal Protection Clauses prohibit the state from justifying laws against same-sex marriage based on the fear that exposing children to homosexuality will encourage them to be lesbian, gay, or bisexual, because the state does not have any legitimate interest in encouraging children to be heterosexual. Part III argues that the Due Process and Equal Protection Clauses prohibit the state from justifying laws against same-sex marriage on purely moral grounds—for similar reasons, and to a similar extent, that the Establishment Clause prohibits the state from justifying such laws on purely religious grounds. While each of these challenges represents a significant contribution to the development of same-sex marriage law, each one also offers a new insight into the meaning of the Due Process and Equal Protection Clauses, thereby contributing to broader developments in the theory and practice of constitutional law. The Article concludes by exploring how these challenges may change the ways that litigants and courts analyze the constitutionality of laws against same-sex marriage and how one of these challenges is likely to be received by the U.S. Supreme Court.