There is no mention of the U.S. Department of Justice in the U.S. Constitution. If that means nothing to you, here are other Dept of Justice agencies that also have NO mention in the U.S. Constitution: 

·         U.S. Attorney General

·         Federal Bureau of Investigation (FBI)

·         Civil Rights Division

·         Antitrust Division

·         Criminal Division

·         Tax Division

·         Drug Enforcement Agency (DEA) 

·         U.S. Marshals Service

The Office of the Attorney General was created by the Judiciary Act of 1789 as a one-person part-time position. The Act specified that the Attorney General was to be "learned in the law," with the duty "to prosecute and conduct all suits in the Supreme Court in which the United States shall be concerned, and to give his advice and opinion upon questions of law when required by the President of the United States, or when requested by the heads of any of the departments, touching any matters that may concern their departments." 

However, the workload became too much for one person, necessitating the hiring of several assistants for the Attorney General. As the work increased along with the size of the new nation, private attorneys were retained to work on cases. By 1870, after the end of the Civil War, the increase in litigation involving the United States required the retention of a large number of private attorneys to handle the workload. 

Congress passed the Act to Establish the Department of Justice creating "an executive department of the government of the United States". The Department of Justice (DOJ) officially came into existence on July 1, 1870. The 1870 Act remains the foundation for the DOJ’s authority. The DOJ, aka the Justice Department, is a Federal Executive Department of the United States government tasked with the enforcement of federal law and administration of justice in the United States.

 The head of the DOJ is the U.S. Attorney General, who reports directly to the President of the United States and who a member of the President's Cabinet. The modern incarnation of the DOJ was created in 1870 during the Ulysses S. Grant Presidency. Some 80 years after the Constitution was ratified.

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The Solicitor General of the United States is the 4^th-highest-ranking official in the U.S. Department of Justice. The U.S. Solicitor General represents the federal government of the United States before the Supreme Court of the United States. The Solicitor General determines the legal position that the United States will take in the Supreme Court. The Solicitor General also files amicus curiae briefs in cases in which the federal government has a significant interest.  

The Solicitor General argues on behalf of the government in every case in which the United States is a party and argues in most of the cases in which the government has filed an amicus brief. In the Federal Courts of Appeal, the Solicitor General reviews cases decided against the United States and determines whether the government will seek review in the Supreme Court. 

The Solicitor General's office reviews cases decided against the United States in the Federal District Courts and approves every case in which the government files an appeal. The U.S. Solicitor General is subservient to, and directly reports to, the United States Attorney General.

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The DOJ is composed of federal law enforcement agencies, including the U.S. Marshals Service, the Federal Bureau of Investigation (FBI), the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), and the Drug Enforcement Administration (DEA) and the Federal Bureau of Prisons.

The primary actions of the DOJ are investigating instances of white collar crime, representing the U.S. government in legal matters (such as in cases before the Supreme Court), and running the federal prison system. The DOJ is also responsible for reviewing the conduct of local law enforcement as directed by the Violent Crime Control and Law Enforcement Act of 1994.

The DOJ is sometimes called "the biggest law firm in the world." It is involved in a lot of matters. The DOJ has more than 114,000 employees and more than 10,000 attorneys. The DOJ an international organization. It has offices in more than 100 countries, in addition to its field offices with the United States and its territories.