First Sergeant is the title given to holders of certain ranks and positions within the United States Armed Forces. While the specifics of the title may differ between the United States Army, Marine Corps and Air Force, all First Sergeants are non-commissioned officers and can be identified by the presence of a diamond, called a "French lozenge," on their rank insignia.

U.S. Army

In the United States Army, the rank of First Sergeant (abbreviated as 1SG) is above Sergeant First Class, below the ranks of Sergeants Major and shares the paygrade of E-8 with Master Sergeant. The rank of First Sergeant carries more responsibility than the rank of Master Sergeant, and the rank may be either given to the soldier upon promotion to the paygrade of E-8 or they may be "laterally promoted" (promoted in rank but not paygrade) from Master Sergeant at a later date. They are also known unofficially as Top Sergeant or just Top, due to the fact that First Sergeants are the most senior non-commissioned officers in an Army company. Not all sergeants bearing the title of First Sergeant actually hold the rank - some may be Sergeants First Class or even Staff Sergeants.

U.S. Marine Corps

In the United States Marine Corps, First Sergeant is one level below Sergeant Major and Master Gunnery Sergeant and is the next rank above Gunnery Sergeant. It is equal in grade to Master Sergeant, although the two ranks have different responsibilities. Unlike the first sergeant and master sergeant programs in the U.S. Army, no lateral movement is possible between the two ranks in the Marine Corps. In their annual performance evaluations, called "proficiency reports," eligible Gunnery Sergeants indicate whether they wish to be considered for promotion to Master Sergeant or First Sergeant, and thus whether they enter the promotional track for Master Gunnery Sergeant or Sergeant Major. .

U.S. Air Force

In the United States Air Force, First Sergeant is a billet held by a senior enlisted member of a military unit who reports directly to the unit commander. This billet may be held by individuals of paygrades E-7 through E-9 (Master Sergeant, Senior Master Sergeant and Chief Master Sergeant), and is denoted on the rank insignia by the French lozenge. Often referred to as the 'first shirt', or 'shirt', the first sergeant is typically responsible for the morale, welfare, and conduct of all the enlisted members under the command of the unit commander.