Chair rail is a type of trim that's installed horizontally along a wall between 2 and 4 feet (61 to 122 centimeters) from the floor [source: Kalyn]. It's primarily used to protect the wall from scratches and dents caused by impacts with chairs. As occupants scoot away from a table, or adjust the placement of a chair, the back of the chair will hit the chair rail instead of the wall. In a home without existing chair rail, new rails can be added to cover minor scratches and damage to the wall.
However, chair rail can also be used to break up a very large or tall wall. An unadorned wall can look too plain or boring, but chair rail can instantly (and subtly) transform the look of a room. It may be used alone or in combination with other types of trim, such as wainscoting or baseboards. Some chair rail is quite elaborate and can be used to complement a traditional or colonial décor. More modern homes will typically benefit most from the clean, straight lines created by simple rounded or square chair rail.