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 Missouri, criminal procedure is governed by a combination of state statutes, the Missouri Rules of Criminal Procedure, and relevant federal laws and constitutional provisions. These rules outline the steps and legal processes from the initial investigation of a crime through to the arrest, charging, trial, and potential conviction or acquittal of a defendant. The U.S. Constitution, particularly the Fourth, Fifth, Sixth, and Fourteenth Amendments, provides the foundation for many procedural protections, such as the right to a fair trial, the right to counsel, protection against self-incrimination, and the right to be free from unreasonable searches and seizures. Missouri's own constitution and statutes also offer additional protections and procedures. For example, the Missouri Revised Statutes contain specific provisions regarding the procedures for arrest, the filing of charges, pretrial release, and discovery. The Missouri Rules of Criminal Procedure further detail the steps in the criminal process, including arraignment, pretrial motions, trial, and sentencing. These rules and laws are interpreted by state and federal courts, and their opinions help shape the application of criminal procedure in Missouri.