A commissariat is a department or organization commanded by a commissary or by a corps of commissaries.
In many countries, commissary is a police rank. In those countries, a commissariat is a police station commanded by a commissary.
In some armies, commissaries are logistic officers. In those countries, a commissariat is a department charged with the provision of supplies, both food and forage, for the troops. The supply of military stores such as ammunition is not included in the duties of a commissariat. In almost every army the duties of transport and supply are performed by the same corps of departmental troops.
In the British Army, the Commissariat was a uniformed civilian service until 1869, when its officers transferred to the new Control Department as commissioned Army officers. The supply organization of the British Army went through a number of incarnations, including the Commissariat and Transport Department, Staff and Corps, before becoming the Army Service Corps in 1888.
In the "Major General's Song" in The Pirates of Penzance by Gilbert and Sullivan, the Major-General boasts that when, among many other bits and pieces of seemingly elementary or irrelevant information, he "know(s) precisely what is meant by commissariat", he will be the best officer the army has ever seen (satirizing 19th century British officers' lack of concrete military knowledge).
Military commissariats of the Soviet Army and modern Russian Army is а local military administrative agency that prepares and executes plans for military mobilization, maintains records on military manpower and economic resources available to the armed forces, provides pre-military training, drafts men for military service, organizes reserves for training, and performs other military functions at the local level.
Among Roman Catholic religious orders, the term Commissariat refers to a division of the Order which is a semi-autonomous body. It is considered less viable than a full Province, but with potential to develop into such, or it serves a group within the Order who are best served separately than in a Province into which they would otherwise be forced, e.g., due to language divisions. As with military usage, the Religious Superior of the division is referred to as the Commissary.