This chapter examines the Supreme Court’s practice, over approximately a century and a half, in developing and applying the “substantive due process” doctrine. The animating premise of that doctrine is that the Due Process Clause confers judicially enforceable protections against substantively unfair infringements of certain “unenumerated” yet fundamental or important rights. After the Court’s embarrassed climb down during the 1930s from a line of decisions enforcing rights to freedom of contract, the Court reembraced the Due Process Clause as a source of “unenumerated” rights in Roe v. Wade (1973) and, later, in decisions protecting rights to engage in private acts of sexual intimacy and extending the unenumerated right to marry to same-sex couples. Although the current Court overturned Roe in Dobbs v. Jackson Women’s Health Organization (2022), the majority opinion avoided a strictly originalist approach by embracing precedents holding that the Due Process Clause protects some fundamental substantive rights that are grounded in “tradition.” The chapter explores the conservative justices’ reasons for adopting that position. It also considers whether substantive due process decisions invalidating prohibitions against sodomy and laws defining marriage as necessarily involving one man and one woman can survive under the rationale of Dobbs.