Arrest or custodial arrest is the process in which the police take physical possession or custody of a person whom they have probable cause to believe committed a criminal offense. Arrest is distinguishable from other circumstances in which the police stop, detain, or otherwise interact with persons because it is generally the point at which a person is not free to leave or walk away from the police. Arrest is also the point at which some Constitutional rights and protections are provided to the accused. A person who is placed in handcuffs or otherwise physically restrained is clearly under arrest—but in some circumstances a person may be under arrest due to threats or intimidation from the police.

In Montana (MT), an arrest or custodial arrest occurs when law enforcement takes a person into physical custody based on probable cause that the individual has committed a criminal offense. This is a formal process that distinguishes from other interactions such as stops or detentions, where the individual still retains the freedom to leave. Once arrested, the individual is not free to leave the presence of the police. The point of arrest triggers certain Constitutional rights and protections for the accused, such as the right to remain silent and the right to an attorney. The use of physical restraints like handcuffs typically signifies an arrest, but an arrest can also occur through verbal commands or actions that reasonably make a person believe they are not free to go, even without physical restraint. Montana law enforcement must adhere to state statutes and federal law, including the Fourth Amendment of the U.S. Constitution, which protects against unreasonable searches and seizures and requires probable cause for an arrest to be lawful.