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 Illinois, criminal procedure is governed by both state statutes and federal law, which outline the processes and rules for the investigation, arrest, charging, and trial of individuals accused of crimes. The Illinois Compiled Statutes (ILCS) contain provisions that regulate various stages of the criminal process, including the Illinois Code of Criminal Procedure. This code sets forth the rights of the accused, procedures for warrants, arraignment, pretrial motions, and trial. Additionally, the U.S. Constitution, particularly the Fourth, Fifth, Sixth, and Fourteenth Amendments, provides protections against unreasonable searches and seizures, the right to due process, the right to a speedy and public trial, the right to counsel, and protection against self-incrimination and double jeopardy. Federal and state court opinions interpret these laws and constitutional protections, ensuring that a defendant's rights are upheld throughout the criminal justice process. It is important for defendants to consult with an attorney who is knowledgeable in both state and federal criminal procedure to navigate these complex legal waters effectively.