Inter-client communication refers to the exchange of information between two or more X clients. This information could be notification of creation of a window, the update of shared data, or perhaps the death of a client. In the UNIX domain, there exists a whole set of inter-process communication (IPC) facilities that can accomplish these tasks. This chapter examines two advanced topics: inter-client communication (ICC) and managing multiple displays. It simply demonstrates how to perform ICC, and does not pretend to present policies. One thing to be aware of when getting involved with ICC mechanisms is that X has a few predefined atoms and property names. For instance, the way clients talk with window managers is through properties. If a person has explored the Intrinsics code or have written an Xlib client, he would have come across a function XSetStandardProperties.