Organisations are engaging in more and more sophisticated business networks to improve collaboration. These business networks can range from more static relationships like Supply Chains to very dynamic networks like virtual organisations. A prerequisite to enable business networks is the interoperability of the participants systems and applications. ATHENA 1 is an Integrated Project funded by the European Commission under Framework Programme 6 that addresses Interoperability of Enterprise Systems and Applications proposing a holistic approach. ATHENA will provide technical results like reference architectures, methodologies and infrastructures complemented by business results that provide ROI calculations and impact predictions for new technologies.