X started as a research project driven by the need to create a hardware-independent display mechanism for Project Athena. This chapter provides a brief history of the X Window System (also called just X), its architecture, a discussion of Xlib, and reasons why Xt is better suited than Xlib for most application development. Project Athena is a major research project being conducted at the Massachusetts Institute of Technology (MIT) to advance the state of technology for distributed systems. This project is heavily financed by International Business Machines (IBM) and the Digital Equipment Corporation (DEC). The ability of X to run on and across different platforms makes it perhaps one of the most innovative technologies to be developed in computing in recent years. And for this very reason, major vendors (IBM, AT&T, DEC, HP, and Sun) have embraced X as their display standard for advanced workstations.