The foundation of American criminal procedure is the U.S. Constitution, including the first 10 amendments, which form the Bill of Rights. The Constitution guarantees all persons living in the United States fundamental rights, freedoms, and liberties. Chief among these, as far as criminal law is concerned, is that defendants are entitled to a presumption of innocence. Defendants do not have to prove their innocence. The government must prove their guilt beyond a reasonable doubt. Rights such as these frame the Federal-State system prescribed in the Constitution. Of particular importance are the Fifth, Sixth, and Eighth Amendments. The Fifth Amendment protects defendants against double jeopardy (being tried more than once for the same crime by the same authority), and against being required to testify against themselves in criminal cases. The Sixth Amendment guarantees defendants a "speedy and public trial by an impartial jury of the State and district wherein the crime shall have been committed." It also entitles defendants to be confronted by and to cross-examine the witnesses against them and to have the "assistance of counsel" for their defense. The Eighth Amendment rules out "excessive bail" for defendants and prohibits "cruel and unusual punishments." This paper describes the Federal criminal justice system, criminal justice at the State and local levels, State and Federal substantive criminal law, and criminal procedure. Sections are also devoted to the following aspects of criminal procedure: right to counsel; bail and pretrial detention; formal accusation and the grand jury; pretrial motions; plea bargaining; right to trial; the trial; sentencing; sanctions; appeal and post-conviction remedies; and parole, remission, and commutation. An overview is provided of juvenile justice in the United States.