A mezzanine (; or in Italian, a mezzanino) is an intermediate floor in a building which is partly open to the double-height ceilinged floor below, or which does not extend over the whole floorspace of the building, a loft with non-sloped walls. However, the term is often used loosely for the floor above the ground floor, especially where a very high-ceilinged original ground floor has been split horizontally into two floors.

Mezzanines may serve a wide variety of functions. Industrial mezzanines, such as those used in warehouses, may be temporary or semi-permanent structures.

In Royal Italian architecture, mezzanino also means a chamber created by partitioning that does not go up all the way to the arch vaulting or ceiling; these were historically common in Italy and France, for example in the palaces for the nobility at the Quirinal Palace.