A curtain wall system is an outer covering of a building in which the outer walls are non-structural.  As the curtain wall is non-structural it can be made of a lightweight material, reducing construction costs.  Curtain wall systems are typically infilled with glass, which provides an architecturally pleasing building, as well as benefits such as daylight.  Other common infills include stone veneer, metal panels, louvres and operable windows or vents.

Curtain walls differ from store-front systems in that they are designed to span multiple floors and take into consideration design requirements such as thermal expansion and contraction; building sway and movement; water diversion and thermal efficiency for cost-effective heating, cooling and lighting in the building.