A Serjeant-at-Arms (also spelt Sergeant-at-Arms) is an officer appointed by a legislative body to keep order during its meetings. The word serjeant is derived from the Latin serviens, which means "servent."

The office originated in Medieval England; the original responsibilities of the Serjeant-at-Arms included "collecting loans and , impressing men and ships, serving on local administration and in all sorts of ways interfering with local administration and justice." [1] Circa 1415, the British House of Commons appointed its first Serjeant-at-Arms.

In the United Kingdom, the Serjeant-at-Arms serves the Speaker of the House of Commons as well as the whole house. He is responsible for maintaining security, law and order within the precincts of Parliament. The Serjeant-at-Arms' symbol of office is the Mace, which functions as a symbol of the Royal authority under which the House of Commons sits. Traditionally, the Serjeant-at-Arms carries the Mace into the House each day as he leads the Speaker's Procession.

In the House of Lords, the Gentleman Usher of the Black Rod is the Serjeant-at-Arms.

Many legislatures, including the United States Congress, have adopted the British practice of appointing Serjeants-at-Arms.