A casement window is a window that is hinged and opens and closes like a book, by swinging either in or out. A casement window consists of a frame, hinges, and a handle or crank that operates the opening and closing mechanism. There are several styles of casement windows.

A typical casement window is vertically hung, hinged on either the left or right side and opens out. A French casement window has two separate panes of glass, hinged on both sides, and opens unobstructed in the center. An awning style casement window is hinged on the top and opens out from bottom up. The casement window was a popular style of window prior to the sash window. They can be found on older style Prairie and Tudor homes.

Though the casement window is not as popular as it once was, replacement casement windows are still being manufactured. A new replacement casement window typically has a crank-style handle, but some have lever style handles that also act as locking mechanisms. Like other styles of windows, the casement window can be installed as a single unit, or grouped together. A casement window is an ideal window to place above cabinets, countertops, or places that are slightly more difficult to reach because the handle mechanisms of casement windows are easy to operate.

Though a casement window may swing in or out, many people avoid the "swinging in" style in spaces that are small because the open window can be an obstruction. Similarly, an inward swinging casement window can interfere with window coverings such as mini-blinds, sheers, or draperies. However, the fact that a casement window swings open makes it easy to clean. Older styles of casement windows usually featured leaded lights, but modern versions typically feature solid pane glass or molded inserts for decoration.

For homeowners who prefer the casement window, new replacement styles are readily available in a wide selection and are considered to be both affordable and energy efficient.