Appellate courts play a major role in the administration of criminal justice in two ways: a person convicted of a crime can have his conviction reviewed for legal error by an appellate court to ensure that appropriate procedures were followed in his individual case, and appellate court decisions in criminal cases are precedent that contribute to the evolution and development of the common law of criminal procedures. This second point merits emphasis, because many very important aspects of criminal procedure can only be understood by being familiar with the recent decisions—and thus the common law—applicable to them. While US criminal procedures in general share many important characteristics, which this book attempts to summarize, they may vary among the various states, and even in the federal system the decisions in the various federal courts of appeals sometimes differ.