Posse Comitatus Act

Posse Comitatus Act

Other short titles	Knott Amendment Posse Comitatus Act of 1878
Long title	An act making appropriations for the support of the Army for the fiscal year ending June thirtieth, eighteen hundred and seventy-nine, and for other purposes.
Nicknames	Army Appropriations Act of 1878
Enacted by	the 45th United States Congress
Effective	June 18, 1878
Citations
Public law	Pub. L.Tooltip Public Law (United States) 45–263
Statutes at Large	20 Stat. 145 aka 20 Stat. 152
Codification
U.S.C. sections created	18 U.S.C. § 1385
Legislative history
Introduced in the House as H.R. 4867 by Herman L. Humphrey (R-WI), William Kimmel (D-MD) on May 13, 1878 Passed the House on May 18, 1878 (130–117) Passed the Senate on June 6, 1878 (36–23) Reported by the joint conference committee on June 15, 1878; agreed to by the House on June 15, 1878 (154–58) and by the Senate on June 15, 1878 (Agreed) Signed into law by President Rutherford B. Hayes on June 18, 1878
Major amendments
1956, 1981, 2021

The Posse Comitatus Act is a United States federal law (18 U.S.C. § 1385, original at 20 Stat. 152) signed on June 18, 1878, by President Rutherford B. Hayes which limits the powers of the federal government in the use of federal military personnel to enforce domestic policies within the United States. Congress passed the Act as an amendment to an army appropriation bill following the end of Reconstruction and updated it in 1956, 1981 and 2021.

The Act originally applied only to the United States Army, but a subsequent amendment in 1956 expanded its scope to the United States Air Force. In 2021, the National Defense Authorization Act for Fiscal Year 2022 further expanded the scope of the Act to cover the United States Navy, Marine Corps, and Space Force. The Act does not prevent the Army National Guard or the Air National Guard under state authority from acting in a law enforcement capacity within its home state or in an adjacent state if invited by that state's governor. The United States Coast Guard (under the Department of Homeland Security) is not covered by the Act either, primarily because although it is an armed service, it also has a maritime law enforcement mission.

The title of the Act comes from the legal concept of posse comitatus, the authority under which a county sheriff, or another law officer, can conscript any able-bodied person to assist in keeping the peace.