The "once-only principle" refers to the idea that citizens and companies only need to submit their data to the administration once. The data should be retrieved from public databases at the request of the citizen or company concerned in subsequent administrative contacts.

The implementation of the once-only principle is a central proposition of the German register modernization [see Registermodernisierung: Zielbild und Umsetzungsplanung].

The EU is also striving for the possibility of a cross-border automated exchange of evidence for various online procedures at the express request of the data subject. In accordance with Art. 14 of the Regulation establishing a single digital gateway, the European Commission is setting up a technical system for this purpose together with the Member States. Its technical and operational specifications are currently being defined in an implementing regulation, but have already been piloted as part of the TOOP ("The Once-Only Principle Project") and DE4A ("Digital Europe For All") projects.