Interoperability is crucial for achieving efficient and effective delivery of cross-boarder and cross-sectoral public services. It directly contributes to the achievement of goals of the Digital Agenda for Europe in particular and the Europe 2020 Strategy in general. In this context, main issues, knowledge units, and legal base of interoperability must be clearly understandable for all who are involved in defining, designing, and implementing Europe-wide public services. While most European countries have developed excellent legislative frameworks and have set up the appropriate institutions for their implementation, the knowledge of the specialized regulations and the necessary skills among the actors involved remain inadequate. The market research performed shows that as the topic of eGovernment and its regulations are quite new, no streamlined system for learning of the target groups (staff of local, regional, and national public administrations, national institutions and agencies, managers of eGovernment projects, developers of public services, policy makers, etc.) in the area of interoperability exists in the countries of the EU. The recently started LLP Leonardo da Vinci project “ELGI- eLearning for eGovernment” addresses this issue and aims at development of an e-learning course for delivering knowledge concerning interoperability. The paper presents work in progress related to the second work package of the mentioned project. Its objective is to study publicly available documents constituting EU policy and reflecting EU practice in the area of interoperability with further use of results in development of the e-learning course. The paper provides summarization of main findings obtained so far and pays attention to the problems impeding development of public services, definition of interoperability, its scope, and beneficiaries, as well as the main most important recently accepted documents and available information sources which can be used for understanding the legal base and the current state in achieving interoperability of public services.