Mapp v. Ohio, 367 U.S. 643 (1961), was a landmark Supreme Court case decided 6–3 by the Warren Court, in which it was held that the Fourth Amendment’s protection against unreasonable searches and seizures applied to the states and excluded unconstitutionally obtained evidence from use in state criminal prosecutions. This decision overruled Wolf v. Colorado, 338 U.S. 25 (1949), and reversed the conviction of appellant Dollree Mapp.
Mapp’s home in Cleveland, Ohio was forcefully entered by police officers who believed that a suspected bomber was inside the house. While searching her home, officers found pornographic books. Later, Mapp was prosecuted under an Ohio statute for knowing possession of lewd and lascivious material. She was convicted even though the prosecution was unable to produce a valid search warrant.
The Supreme Court’s majority held that all evidence obtained unconstitutionally, without a search warrant, is inadmissible in state criminal prosecutions. Such evidence was already barred in federal courts, and the majority agreed that the exclusionary rule for unlawfully seized evidence applied to state courts through the Fourteenth Amendment. The Supreme Court insisted that the exclusionary rule had to apply to the states, or else the Fourth Amendment was essentially "a form of words."
[Last reviewed in October of 2025 by the Wex Definitions Team]