Mapp v. Ohio, the Exclusionary Rule, and Constitutional Judicial Review

Mapp v. Ohio is the US Supreme Court opinion that imposed the Fourth Amendment exclusionary rule on the states. Mapp overruled earlier cases by holding that evidence obtained by unreasonable government searches and seizures was not admissible in state or local criminal prosecutions, just as it had long been inadmissible in federal cases. It is hard to overstate the impact of this decision, which changed the rules and procedures both for policing and for litigation in criminal cases throughout the United States. But Mapp’s significance extends beyond its specific holding. It adopted an interpretive method, often labeled “selective incorporation,” employed by the Supreme Court in subsequent decisions, that imposed specific provisions contained in the Bill of Rights, the first eight amendments to the Constitution upon the states. These decisions redefined federalism in the United States by establishing federal authority over government actions previously governed by state law. In the realm of search and seizure law, by requiring states to adhere to the Supreme Court’s search and seizure opinions, Mapp also generated potent political and legal opposition. In subsequent opinions the Supreme Court limited the exclusionary rule’s scope, diluting Mapp’s impact on police practices by reducing the situations in which federal constitutional rules required exclusion of evidence.