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 Iowa, criminal procedure is governed by both state statutes and federal law, which outline the processes for investigation, arrest, charging, and the trial of criminal defendants. The Iowa Rules of Criminal Procedure provide detailed instructions on how criminal proceedings should be conducted in the state. These rules cover various stages of the criminal process, including the issuance of warrants, arraignment, pretrial motions, plea bargaining, trial, and sentencing. Additionally, the U.S. Constitution, particularly the Fourth, Fifth, Sixth, and Fourteenth Amendments, plays a crucial role in protecting the rights of criminal defendants. These constitutional protections ensure the right to a fair trial, the right against self-incrimination, the right to due process, and the right to effective counsel, among others. Iowa courts interpret and apply these rules and constitutional rights to ensure that the criminal justice system operates fairly and justly. Federal rules and court opinions also impact Iowa's criminal procedure, especially in cases where federal law is implicated or where constitutional rights are at issue.