Despite the large and ongoing investments in information systems and technologies, many organizations still suffer from the lack of integration and interoperability of multiple information systems, In order to deal with these enduring problems, a number of government organizations and corporate firms in the United States have developed and maintained IT architectures through enterprise architecture planning. An IT architecture is a decision-making framework for IT planners and developers, establishing guidelines for the individual IT resource owners and users. It provides guidance to those involved in building and maintaining IT systems and infrastructure. Enterprise architecture planning represents a new paradigm of information systems planning in that it addresses the long-term view of the enterprise organization from top-level principles to detailed technology architectures. This paper explores a couple of cases in the successful implementation of IT architectures in both public and private sectors, and proposes a step-by-step methodology for building an effective IT architecture.