Most enterprise IT systems are very complex with a combination of COBOL and Java programs running on multiple platforms. What is needed is a solid IT architecture that supports the operation and growth of a cross-platform IT system. It must enable the iterative and incremental development of applications that are foreseen in an agile development process. The design concept of such an architecture with its infrastructure and development tool is presented in this chapter. This design concept is based on the design principles and architectural patterns of software engineering. The architecture is a combination of layered, component-based, and service-oriented architectural patterns. The agile development process is based on a model-driven approach. The architecture and development approaches were first introduced in 2004. Since then, many applications have been developed on time and within budget.