As more and more information becomes accessible via on-line databases, more public services can be provided and more complex queries involving several registers become feasible as well. However, not all of the digitally stored data is public and thus strict access control mechanisms must be enforced. At the same time, in order to take full advantage of on-line data sources, high availability must be achieved as well. This paper describes an infrastructure developed in Estonia to satisfy these somewhat contradictory requirements. This infrastructure (called X-Road) enables different organizations to access each other's data and rely on it when taking legally binding decisions. We discuss technical details of X-Road together with the issues arising when the infrastructure is to be implemented on national or international level.