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 Washington State, criminal procedure is governed by a combination of state statutes, the Washington Rules of Criminal Procedure, and federal laws, including constitutional protections afforded to all citizens. These procedures outline the steps from the initial investigation of a crime to the arrest, charging, trial, and potential conviction or acquittal of a defendant. The Washington State Constitution, along with the United States Constitution, particularly the Fourth, Fifth, Sixth, and Fourteenth Amendments, provide the framework for ensuring that a defendant's rights are protected throughout the criminal justice process. This includes the right to a fair and speedy trial, the right to counsel, protection against self-incrimination, and the right to be free from unreasonable searches and seizures. State and federal court opinions continually interpret and apply these rights to ensure that criminal procedures are conducted fairly and justly, in accordance with both state and federal law.