The Fourth Amendment to the United States Constitution is part of the Bill of Rights. It prohibits unreasonable searches and seizures. In addition, it sets requirements for issuing warrants: warrants must be issued by a judge or magistrate, justified by probable cause, supported by oath or affirmation, and must particularly describe the place to be searched and the persons or things to be seized.
In United States criminal law, probable cause is the standard by which police authorities have reason to obtain a warrant for the arrest of a suspected criminal or the issuing of a search warrant. There is no universally accepted definition or formulation for probable cause. One traditional definition, which comes from the U.S. Supreme Court's 1964 decision Beck v. Ohio, is when "whether at [the moment of arrest] the facts and circumstances within [an officer's] knowledge and of which they had reasonably trustworthy information [are] sufficient to warrant a prudent [person] in believing that [a suspect] had committed or was committing an offense."
Mapp v. Ohio, 367 U.S. 643 (1961), was a landmark decision of the U.S. Supreme Court in which the Court ruled that the exclusionary rule, which prevents prosecutors from using evidence in court that was obtained by violating the Fourth Amendment to the U.S. Constitution, applies not only to the federal government but also to the U.S. state governments. The Supreme Court accomplished this by use of a principle known as selective incorporation; in Mapp this involved the incorporation of the provisions, as interpreted by the Court, of the Fourth Amendment which is applicable only to actions of the federal government into the Fourteenth Amendment's due process clause which is applicable to actions of the states.
Terry v. Ohio, 392 U.S. 1 (1968), was a landmark U.S. Supreme Court decision in which the Court ruled that it is constitutional for American police to "stop and frisk" a person they reasonably suspect to be armed and involved in a crime. Specifically, the decision held that a police officer does not violate the Fourth Amendment to the U.S. Constitution's prohibition on unreasonable searches and seizures when questioning someone even though the officer lacks probable cause to arrest the person, so long as the police officer has a reasonable suspicion that the person has committed, is committing, or is about to commit a crime. The Court also ruled that the police officer may perform a quick surface search of the person's outer clothing for weapons if they have reasonable suspicion that the person stopped is "armed and presently dangerous." This reasonable suspicion must be based on "specific and articulable facts," and not merely upon an officer's hunch.
Stanley v. Georgia, 394 U.S. 557 (1969), was a U.S. Supreme Court decision that helped to establish an implied "right to privacy" in U.S. law in the form of mere possession of obscene materials.
Atwater v. Lago Vista, 532 U.S. 318 (2001), was a United States Supreme Court decision which held that a person's Fourth Amendment rights are not violated when the subject is arrested for driving without a seatbelt. The court ruled that such an arrest for a misdemeanor that is punishable only by a fine does not constitute an unreasonable seizure under the Fourth Amendment.
United States v. Leon, 468 U.S. 897 (1984), was a United States Supreme Court case in which the Court established the "good faith" exception to the Fourth Amendment exclusionary rule.
Chimel v. California, 395 U.S. 752 (1969), was a 1969 United States Supreme Court case in which the Court held that police officers arresting a person at home could not search the entire home without a search warrant, but police may search the area within immediate reach of the person without a warrant. The rule on searches incident to a lawful arrest within the home is now known as the Chimel Rule.
Ker v. California, 374 U.S. 23 (1963), was a case before the United States Supreme Court, which incorporated the Fourth Amendment's protections against illegal search and seizure. The case was decided on June 10, 1963, by a vote of 5–4.
Aguilar v. Texas, 378 U.S. 108 (1964), was a decision by the United States Supreme Court, which held that "[a]lthough an affidavit supporting a search warrant may be based on hearsay information and need not reflect the direct personal observations of the affiant, the magistrate must be informed of some of the underlying circumstances relied on by the person providing the information and some of the underlying circumstances from which the affiant concluded that the informant, whose identity was not disclosed, was credible or his information reliable." Along with Spinelli v. United States (1969), Aguilar established the Aguilar–Spinelli test, a judicial guideline for evaluating the validity of a search warrant based on information provided by a confidential informant or an anonymous tip. The test developed in this case was subsequently rejected and replaced in Illinois v. Gates, 462 U.S. 213 (1983).
Cupp v. Murphy, 412 U.S. 291 (1973), was a United States Supreme Court case in which the Court upheld a murder conviction notwithstanding a challenge that the evidence upon which guilt was based was obtained in violation of the Fourth and Fourteenth Amendments of the United States Constitution. The court held that in view of the station-house detention upon probable cause, the very limited intrusion of scraping the defendant's fingernails for blood and other material, undertaken to preserve highly evanescent evidence, did not violate the Fourth and Fourteenth Amendments.
Ornelas v. United States, 517 U.S. 690 (1996), was a case decided by the Supreme Court of the United States that held that appellate courts should review probable cause determinations for warrantless searches de novo.
Stoner v. California, 376 U.S. 483 (1964), is a United States Supreme Court decision involving the Fourth Amendment. It was a criminal case appealed from the California Courts of Appeal after the California Supreme Court denied review. The case extended the situations under which search warrants are required as they reversed a robbery conviction made on the basis of evidence obtained in violation of the holding.
Kentucky v. King, 563 U.S. 452 (2011), was a decision by the US Supreme Court, which held that warrantless searches conducted in police-created exigent circumstances do not violate the Fourth Amendment as long as the police did not create the exigency by violating or threatening to violate the Fourth Amendment.
Maryland v. King, 569 U.S. 435 (2013), was a decision of the United States Supreme Court which held that a cheek swab of an arrestee's DNA is comparable to fingerprinting and therefore, a legal police booking procedure that is reasonable under the Fourth Amendment.
Elkins v. United States, 364 U.S. 206 (1960), was a US Supreme Court decision that held the "silver platter doctrine", which allowed federal prosecutors to use evidence illegally gathered by state police, to be a violation of the Fourth Amendment to the United States Constitution.
Ybarra v. Illinois was a decision of the U.S. Supreme Court which ruled that a warrant can not be used to search an unnamed individual unless the warrant mentions that unnamed parties are involved or exigent circumstances are shown to exist.
Abel v. United States, 362 U.S. 217 (1960), was a United States Supreme Court case.
Nieves v. Bartlett, 587 U.S. ___ (2019), was a civil rights case in which the Supreme Court of the United States decided that probable cause should generally defeat a retaliatory arrest claim brought under the First Amendment, unless officers under the circumstances would typically exercise their discretion not to make an arrest.
Johnson v. United States, 333 U.S. 10 (1948), was a significant United States Supreme Court decision addressing search warrants and the Fourth Amendment. In this case, where federal agents had probable cause to search a hotel room but did not obtain a warrant, the Court declared the search was "unreasonable."
