United States attorneys are officials of the U.S. Department of Justice who serve as the chief federal law enforcement officers in each of the 94 U.S. federal judicial districts. Each U.S. attorney serves as the United States' chief federal criminal prosecutor in their judicial district and represents the U.S. federal government in civil litigation in federal and state court within their geographic jurisdiction. U.S. attorneys must be nominated by the president and confirmed by the Senate, after which they serve four-year terms.

Currently, there are 93 U.S. attorneys in 94 district offices located throughout the United States, Puerto Rico, the U.S. Virgin Islands, Guam, and the Northern Mariana Islands. One U.S. attorney is assigned to each of the judicial districts, with the exception of Guam and the Northern Mariana Islands, where a single U.S. attorney serves both districts. Each U.S. attorney is the chief federal law enforcement officer within a specified jurisdiction, acting under the guidance of the United States Attorneys' Manual. They supervise district offices with as many as 350 assistant U.S. attorneys (AUSAs) and as many as 350 support personnel.

U.S. Attorney's Offices are staffed mainly by assistant U.S. attorneys (AUSA). Often colloquially called "federal prosecutors", assistant U.S. attorneys are government lawyers who act as prosecutors in federal criminal trials and as the United States federal government's lawyers in civil litigation in which the United States is a party. In carrying out their duties as prosecutors, AUSAs have the authority to investigate persons, issue subpoenas, file formal criminal charges, plea bargain with defendants, and grant immunity to witnesses and accused criminals.

U.S. attorneys and their offices are part of the Department of Justice. U.S. attorneys receive oversight, supervision, and administrative support services through the Justice Department's Executive Office for United States Attorneys. Selected U.S. attorneys participate in the Attorney General's Advisory Committee of United States Attorneys.

The Office of the United States Attorney was created by the Judiciary Act of 1789, along with the office of Attorney General and United States Marshal. The same act also specified the structure of the Supreme Court of the United States and established inferior courts making up the United States Federal Judiciary, including a district court system. Thus, the office of U.S. Attorney is older than the Department of Justice. The Judiciary Act of 1789 provided for the appointment in each judicial district of a "Person learned in the law to act as attorney for the United States...whose duty it shall be to prosecute in each district all delinquents for crimes and offenses cognizable under the authority of the United States, and all civil actions in which the United States shall be concerned..." Prior to the existence of the Department of Justice, the U.S. attorneys were independent of the attorney general, and did not come under the AG's supervision and authority until 1870, with the creation of the Department of Justice.

U.S. attorneys are appointed by the president of the United States for a term of four years, with appointments subject to confirmation by the Senate. A U.S. attorney continues in office, beyond the appointed term, until a successor is appointed and qualified. By law, each United States attorney is subject to removal by the president. The attorney general has had the authority since 1986 to appoint interim U.S. attorneys to fill a vacancy.

The governing statute, 28 U.S.C. § 546 provided, up until March 9, 2006:

(c) A person appointed as United States attorney under this section may serve until the earlier of—