A window manager is computer software that controls the placement and appearance of windows within a windowing system in a graphical user interface. Most window managers are designed to help provide a desktop environment. They work in conjunction with the underlying windowing system which provides required functionality such as support for graphics hardware, pointing devices, and a keyboard, and are often written and created using a widget toolkit.

Few window managers are designed with clear distinction between the windowing system and the window manager. Every graphical operating system which uses a windows metaphor has some form of window management, however in practice the elements of this functionality vary greatly. The elements usually associated with window managers are those which allow the user to open, close, minimize, maximize, move, resize, and keep track of running windows, including window decorators. Many window managers also come with docks, task bars, program launchers, desktop icons, and wallpaper.