Criminal procedure is the process related to the investigation, arrest, charging, and conviction or acquittal of a criminal defendant. Much of criminal procedure is comprised of processes and rules through which the government (state, federal, or municipal) enforces substantive criminal law and through which a criminal defendant’s Constitutional and other rights are protected.

The law of criminal procedure is primarily located in the applicable state or federal rules of criminal procedure and state and federal court opinions interpreting and applying Constitutional and other legal rights.

In Massachusetts, criminal procedure is governed by both state and federal laws, which outline the processes for investigation, arrest, charging, and the eventual conviction or acquittal of a criminal defendant. The Massachusetts Rules of Criminal Procedure provide detailed procedures for the courts in criminal cases, including arraignment, pre-trial motions, trial, and sentencing. These rules are designed to ensure fair and orderly proceedings. The U.S. Constitution, particularly the Fourth, Fifth, Sixth, and Fourteenth Amendments, plays a crucial role in protecting the rights of defendants, such as the right to due process, the right to a speedy and public trial, the right to counsel, and protection against unreasonable searches and seizures. Massachusetts courts interpret and apply these constitutional protections, as well as state-specific rights found in the Massachusetts Declaration of Rights. Additionally, decisions from the Supreme Judicial Court of Massachusetts and the Massachusetts Appeals Court contribute to the body of law that shapes criminal procedure in the state.