Riley v. California, 573 U.S. 373 (2014), is a landmark United States Supreme Court case in which the court ruled that the warrantless search and seizure of the digital contents of a cell phone during an arrest is unconstitutional under the Fourth Amendment.

The case arose from inconsistent rulings on cell phone searches from various state and federal courts. The Fourth, Fifth, and Seventh Circuits had ruled that police officers can search cell phones incident to arrest under various standards. That rule was also accepted by the state supreme courts of Georgia, Massachusetts, and California. On the other hand, the First Circuit and the state supreme courts of Florida and Ohio disagreed and ruled that police needed a warrant to search the information on a suspect's phone. California had also proposed a state statute requiring police to obtain a warrant before searching the contents of "portable electronic devices".

The U.S. Supreme Court took the Riley case in order to address these inconsistencies at the lower courts. Riley has been widely praised as “a sweeping victory for privacy rights” with legal scholars describing the decision as "the privacy gift that keeps on giving."

In Chimel v. California (1969), the Supreme Court ruled that if the police arrest someone, they may search the body of the person without a warrant and "the area into which he might reach" in order to protect material evidence or for the officers' safety. That ruling served as confirmation of the notion that police may search a suspect, and the area immediately surrounding that person, without a warrant during a lawful arrest in accordance with the search incident to arrest doctrine.

Before the Riley case, the Supreme Court had explored variations on the Chimel theme, considering police searches of various items individuals had close at hand when arrested, and the court was prepared to look into the seizure of cell phones when incident to arrest. Lower courts were in dispute on whether the Fourth Amendment allows the police to search the digital contents of such a phone, without first getting a warrant.

Stanford University law professor Jeffrey L. Fisher, who represented Riley in court, explaining in a media interview that at least six courts held that the Fourth Amendment permits searches of this type, but that three courts did not. Therefore, a definitive Supreme Court precedent was needed. Fisher opined that there are "very, very profound problems with searching a smartphone without a warrant" and that it was like giving "police officers authority to search through the private papers and the drawers and bureaus and cabinets of somebody's house." Fisher warned that it could open up "every American's entire life to the police department, not just at the scene but later at the station house and downloaded into their computer forever".

David Leon Riley was pulled over in San Diego, California in 2009 for expired registration tags on his vehicle. The police officer then found that Riley was driving with a suspended driver's license. The San Diego Police Department's policy at the time was to impound a vehicle after stopping a driver with a suspended license in order to prevent them from driving again. Additionally, department policy required officers to perform an inventory search of the vehicle, which in Riley's case led to the discovery of two handguns under the hood of his vehicle.

Later ballistic testing confirmed that the handguns were the weapons used in a gangland murder that had taken place a few weeks previously, for which Riley had been a suspect. Because of the discovery of the concealed and loaded handguns, along with gang paraphernalia, during the vehicle search, police placed Riley under arrest and searched his cell phone without a warrant.