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 Pennsylvania, criminal procedure is governed by both state and federal laws that outline the processes for investigation, arrest, charging, and the eventual conviction or acquittal of a criminal defendant. The Pennsylvania Rules of Criminal Procedure provide detailed procedures for pretrial, trial, and post-trial processes, including arraignment, pretrial motions, plea bargaining, and sentencing. These rules are designed to ensure that a defendant's constitutional rights, such as the right to a fair trial, the right to counsel, and protection against self-incrimination, are upheld throughout the criminal justice process. Additionally, federal rules and constitutional protections, such as those found in the Fourth, Fifth, Sixth, and Fourteenth Amendments, apply to criminal proceedings in Pennsylvania. Court opinions from both state and federal courts interpret these laws and rights, and they can set precedents that affect future criminal procedures. It is important for defendants to have an attorney who is knowledgeable about both state and federal criminal procedure to navigate the complexities of the legal system.