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

The curtain wall system is designed to withstand wind and earthquake loads, reduce air leakage, control vapor diffusion, avoid rain penetration, prevent surface and cavity condensation, and limit excessive heat loss or heat gain. It is also designed to resist noise and fire.