Mugler v. Kansas, 123 U.S. 623 (1887), was an important United States Supreme Court case in which the 8–1 opinion of Associate Justice John Marshall Harlan and the lone partial dissent by Associate Justice Stephen Johnson Field laid the foundation for the Supreme Court's later acceptance and defense during the Lochner era of Justice Field's theory of economic substantive due process under the Due Process Clause of the Fourteenth Amendment. The companion case was Kansas v. Ziebold & Hagelin.