The U.S. justice system consists of three branches of government: legislative, executive, and judicial branches. Each of these branches exists at local, state, and federal levels of government. The three primary components of the U.S. criminal justice system are the police, corrections, and court systems. The police are responsible for carrying out law enforcement, order maintenance, and public service functions. The largest segment of police responsibility is at the local level, while the smallest is at the state level. Federal police agencies exist to handle specialized issues defined by Congress or the President. In the judicial process, police have responsibilities that include investigating crimes, gatekeeping for court materials, and court transport and security.
There is a lot of variation among U.S. court systems. The primary functions of courts are to protect society from criminal offenders and to resolve interpersonal disputes.
The corrections system is responsible for individuals on probation and parole; people in community corrections programs; and people in corrections facilities. Theories for sentencing criminal offenders include retribution, which allows payback for past crimes; rehabilitation, which strives to make offenders productive members of society; general and specific deterrence, which attempt to prevent the public and the offender, respectively, from committing future offenses; incapacitation, which prevents reoffending through removal from society; and reintegration, which prepares offenders to reenter society. Most correctional activity occurs at the state level.
The three branches of government have a separation of powers. They have checks and balances on one another, yet are interdependent. The legislative branch (Congress) has powers that include taxation, declaration of war, and establishment of the armed forces. The executive branch (the President) has the power to enforce the laws, act as commander-in-chief of the armed forces, and appoint executive offices. The judiciary branch (U.S. Supreme Court) has the power of judicial review. Some powers are exercised by the federal government, and others by the state governments. This division of power is known as federalism.
A court's power to hear a case is called jurisdiction. Subject matter jurisdiction primarily refers to whether a court has jurisdiction over criminal or civil matters. Courts have limited jurisdiction if they lack the power to hear a full range of cases, and general jurisdiction if they can hear a full range of cases. The first court to hear a case is the court of original jurisdiction. A court of appellate jurisdiction hears appeals on errors of law from the courts of original jurisdiction.
The law is able to provide many forms of relief for court parties, including damages and criminal sentences. When the law is unable to provide a remedy, a party may find relief in equity, which is usually in the form of injunctions. The U.S. utilizes an adversarial justice system in which there are two opposing parties in a zero-sum game. This contrasts with the inquisitional justice model, in which both the judge and prosecutor devote their efforts to producing evidence against the defendant.