A curtain wall system is an outer covering of a building in which the outer walls are non-structural, but merely keep the weather out and the occupants in. As the curtain wall is non-structural it can be made of a lightweight material, reducing construction costs. When glass is used as the curtain wall, a great advantage is that natural light can penetrate deeper within the building.

Curtain-wall systems are typically designed with extruded aluminum members. The aluminium frame is typically in filled with glass, which provides an architecturally pleasing building, as well as benefits such as day lighting.Curtain walls are key component of commercial building envelope construction - from major high-rise office towers to custom skylights.