The Judiciary Act of 1789 created the Office of Attorney General of the United States. By 1870, and largely as a result of the Civil War, the Department of Justice was created to handle the growing number of criminal prosecutions and civil cases in which the United States had an interest.
The Judiciary Act of 1789 authorizes the U.S. Attorney General to issue opinions on questions of law if requested by the President or Executive Branch departments. The authority to give legal opinions has been delegated to the Office of Legal Counsel (OLC) by the U.S. Attorney General. This authority is codified at 28 U.S.C. §§ 510–513.
Selected published opinions are available on the OLC website. Published opinions are also accessible on Lexis and Westlaw.
Hein Online has a library that includes the Opinions of the Office of Legal Counsel and the Official Opinions of the Attorneys General of the United States. The Hein library also has state attorney general opinions.
The Office of Information Policy (OIP) oversees compliance by all federal agencies with the requirements of the Freedom of Information Act.
The Office of Public Affairs (OPA) is the main contact point for the DOJ and the news media. "The Office is responsible for ensuring that the public is informed about the Department's activities and about the priorities and policies of the Attorney General and the President with regard to law enforcement and legal affairs." (from the website)