Last year, in District of Columbia v. Heller, the Supreme Court confirmed what most scholars and a substantial majority of Americans long believed: that the Second Amendment protects an individual right to keep and bear arms. Heller led to the current challenge to Chicago’s handgun ban, which raises the question of whether the Fourteenth Amendment protects that right against infringement by state and local governments. The Seventh Circuit answered the question in the negative, finding itself foreclosed by 19th-century Supreme Court decisions. The Supreme Court has agreed to review the case and specifically consider whether the Fourteenth Amendment’s Due Process Clause or its Privileges or Immunities Clause is the proper provision for incorporating the Second Amendment right to keep and bear arms as against the states. Cato, joined by the Pacific Legal Foundation, has filed a brief supporting those challenging the handgun ban—who are represented by Alan Gura, who successfully argued Heller—and calling for an overruling of the Slaughter-House Cases, which eviscerated the Privileges or Immunities Clause in 1873. Slaughter-House narrowly circumscribed the rights protected by the Privileges or Immunities Clause, contrary to the intentions of the Amendment’s framers and in direct contradiction to the developments in legal theory that underlay its adoption. We also argue that in addition to ignoring the history surrounding the Fourteenth Amendment, the Slaughter-House majority violated basic rules of constitutional interpretation. Finally, restoring the Privileges or Immunities Clause would not result in the demise of substantive due process because the idea at the core of that doctrine—that the Due Process Clause imposes something more than mere procedural limits on government power—was widely accepted when the Fourteenth Amendment was enacted and its authors rightly believed that the Due Process and the Privileges or Immunities Clauses would provide separate but overlapping protections for individual rights.