Despite current advancements in online provision of eGovernment services, interoperability issues at national and crosscountry level that will facilitate fully integrated, both vertically and horizontally, one-stop, electronic services still remain unsolved. In this context, eGovernment Interoperability Frameworks try to continually extend their scope and to outline the essential prerequisites for joined-up and web-enabled e-government in order to effectively second the seamless exchange of information and the deployment of interoperable systems in the public sector. This paper presents the national interoperability frameworks that have been released by 9 countries (Australia, Belgium, Denmark, Estonia, Germany, Greece, New Zealand, United Kingdom and United States of America) and have reached a certain degree of maturity. A comparative analysis among their contents is conducted in order to indicate the similarities and differences in their philosophy and implementation and to provide a set of recommendations for any interesting party embarking to design or update an Interoperability Framework.