The need for centralized e-Government strategies and policies is a fertile ground for the development of e-Government INTEROPERABILITY FRAMEWORKS (eGIFs). Integrated information systems and one-stop public services to citizens and businesses are heavily dependent on the resolution of the ever-expanding interoperability challenge and the satisfaction of public services' stakeholders. This can only be realistically addressed if the scope of eGIFs is widened, to include service composition and discovery, security standards, certification of public sites, as well as unified data models for achieving a common understanding of semantics at a syntax-independent level. The Greek eGIF presents a transition from paper-based specifications to a robust system that acts as a repository of systems, services, data schemas, certification tools and training material. This paper presents the objectives, the overall methodology and the architecture of the Greek eGIF, that meets today's demands for modelling, storing, managing and updating a vast number of eGovernment-related information.