An enterprise architecture (EA) provides a clear and comprehensive picture of the structure of an entity, whether an organization or a functional or mission area. It is an essential tool for effectively and efficiently engineering business processes and for implementing and evolving supporting systems. The concept of an architecture to describe an enterprise first emerged in the mid-1980s, and over the years various frameworks2 for defining the content of EAs have been published. Our work in the early 1990s identified architectures as a critical success factor allowing organizations to effectively apply information technology (IT) to meet mission goals. Since then, we have worked with the Congress, the Office of Management and Budget (0MB), and the federal Chief Information Officers (ClO) Council to recognize the importance of architectures and assist agencies in developing, maintaining, and using them. In our reviews of agency IT management practices and major systems modernization programs, we continue to identify the lack of an architecture as a major management weakness, and we have made numerous recommendations addressing this important area.