X-Road enables the Once-Only Principle by allowing public authorities to securely reuse data that already exists in trusted national registers. Instead of asking citizens or businesses to submit the same information repeatedly, an authority can request the required data directly from the authoritative source, with every exchange authenticated, encrypted, logged and governed.

Within a country, X-Road connects government agencies, municipalities and other trusted organisations into a secure data exchange ecosystem. Each organisation retains control of its own systems and data, while X-Road provides the interoperability, security and auditability required for real-time data sharing.

X-Road can also support cross-border once-only services by connecting the national data exchange ecosystem to the EU’s Once-Only Technical System (OOTS) via a gateway component. The EU OOTS enables public administrations to retrieve evidence from another Member State at the user’s explicit request, helping citizens and businesses complete cross-border procedures without resubmitting documents already held by public authorities.

In this model, X-Road serves as the trusted national backbone, while the gateway component connects national services to the EU OOTS. Together, they enable once-only data exchange both within the country and across EU borders. Similarly, an X-Road ecosystem serving as an OOTS at the state level can be connected to a federal-level OOTS.