This chapter will explain how the Unix GUI stack fits together. By the time you are finished reading it, you will understand how Unix programs, libraries, and system services cooperate to throw graphics and text on a screen and handle input events. You will be aware of the major alternatives at each level of the stack, and be prepared to learn any of the specific APIs needed to use them. You will also have some knowledge of the sorts of construction tools that are available to automate GUI coding.