A billet is a term for living quarters to which a soldier is assigned to sleep. Historically, it referred to a private dwelling that was required to accept the soldier.

Soldiers are generally billeted in barracks or garrisons when not on combat duty, although in some armies soldiers with families are permitted to maintain a home off-post. Used for a building, the term is more commonly used in British English; United States standard terms are quarters, barracks, "Single (Soldier) Housing" or "Family Housing".

Originally, a "billet" (from the French) was a note, commonly used in the 18th and early 19th centuries as a "billet of invitation." A particular use of the word in this sense is to denote an order issued to a soldier entitling him to quarters with a certain person. From this meaning, the word billet came to be loosely used of the quarters thus obtained. Repeated petitions against the practice of billeting, starting in the 16th century, culminated in its outlawing in 1689 as an extension of a section of the Petition of Right 1628.