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 New Hampshire, criminal procedure is governed by both state statutes and the New Hampshire Rules of Criminal Procedure. These rules outline the steps and processes from investigation to trial, including arrest, arraignment, pre-trial motions, plea bargaining, trial, and sentencing. The U.S. Constitution, particularly the Fourth, Fifth, Sixth, and Fourteenth Amendments, provides the foundation for the rights of criminal defendants, such as the right to due process, the right to a speedy and public trial, the right to counsel, and protection against self-incrimination and unreasonable searches and seizures. New Hampshire's Constitution also affords additional protections to individuals within the state. Federal law and U.S. Supreme Court decisions further influence New Hampshire's criminal procedure by interpreting constitutional rights and setting minimum standards that states must follow. An attorney representing a defendant in New Hampshire must navigate both state and federal laws to ensure that the defendant's rights are protected throughout the criminal justice process.