An arrest warrant is a written order from a judge or magistrate that commands the police or other authority to physically take a person accused of a criminal offense into custody. The Fourth Amendment to the United States Constitution requires an arrest warrant to be supported by probable cause—which means there is a reasonable basis to believe the person to be arrested committed a crime.

Arrest warrants protect people from unlawful arrests by requiring the independent review of supporting facts by a person (judge or magistrate) who is not involved in the process of investigating the alleged crime. Arrest warrants also give the accused actual notice of the charge of a criminal offense committed by the accused. Arrest warrants are generally required to take an accused into physical custody unless there is an exception to the warrant requirement—such as when the crime is committed in the presence of the arresting officer.

In Missouri, as in other states, an arrest warrant is a legal document issued by a judge or magistrate that authorizes law enforcement to take an individual into custody on suspicion of a crime. The issuance of an arrest warrant in Missouri must be based on probable cause, which is a reasonable belief, supported by facts and circumstances, that the individual has committed a criminal offense. This requirement is in line with the Fourth Amendment of the U.S. Constitution, which protects individuals against unreasonable searches and seizures. The process of obtaining an arrest warrant involves law enforcement presenting evidence to a judge or magistrate, who then independently reviews the evidence to determine if probable cause exists. If the judge is satisfied that the legal threshold has been met, they will issue the warrant. Exceptions to the warrant requirement do exist, such as when a crime is witnessed by a police officer, which allows for an arrest to be made without a warrant. Arrest warrants serve to limit police powers and ensure that individuals' rights are protected by providing a neutral evaluation of the need for arrest and by notifying the accused of the charges against them.