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.

n. sufficient reason based upon known facts to believe a crime has been committed or that certain property is connected with a crime. Probable cause must exist for a law enforcement officer to make an arrest without a warrant, search without a warrant, or seize property in the belief the items were evidence of a crime. While some cases are easy (pistols and illicit drugs in plain sight, gunshots, a suspect running from a liquor store with a clerk screaming "help"), actions "typical" of drug dealers, burglars, prostitutes, thieves, or people with guilt "written across their faces," are more difficult to categorize. "Probable cause" is often subjective, but if the police officer's belief or even hunch was correct, finding stolen goods, the hidden weapon or drugs may be claimed as self-fulfilling proof of probable cause. Technically, probable cause has to exist prior to arrest, search or seizure. See also: Bill of Rights search search and seizure