Tier-on-tier windows are a type of window treatment that consists of two sets of overlapping shutters mounted on a window. The top tier is typically fixed in place and the bottom tier is hinged, allowing it to be opened and closed as needed. Tier-on-tier windows are often used for decorative purposes as well as for controlling light, privacy, and temperature in a room.

They can be made of various materials such as wood, plastic, or metal and can be finished in a variety of colors and styles to match the decor of a home. Tier-on-tier windows are a popular choice for traditional and period-style homes, as they add a classic, elegant look to a room.