In U.S. law, the principle that evidence seized by police in violation of the constitutional protection against unreasonable search and seizure may not be used against a criminal defendant at trial.
The Supreme Court of the United States established the validity of the rule in Weeks v. U.S. (1914). In Wolf v. Colorado (1949) the court limited application of the rule to the federal courts; this decision was overturned in Mapp v. Ohio (1961), which required the rule to be applied universally. In the 1980s the court allowed an exception to the rule, holding that evidence obtained "in good faith" with a search warrant later ruled invalid is admissible.