A window system is a standard part of a computer's graphical user interface, as opposed to a command line interface. It developed as a part of the WIMP paradigm invented at Xerox PARC. A window system enables the computer user to work with several programs at the same time. Each program runs in its own window, which is a rectangular area of the screen. Most window systems allow windows to overlap, and provide means for the user to perform standard operations such as moving/resizing a wnidow, sending a window to the foreground/background, minimizing/maximizing a window, etc. From a programmer's point of view, a window system implements graphical primitives such as rendering fonts or drawing a line on the screen, effectively providing an abastraction of the graphics hardware. Some window systems, like X have advanced capabilities such as network transparency, allowing the user to run graphical applications on a remote machine.

See also window manager, Microsoft Windows, GEM