The Once-Only Principle Project (TOOP) ended on 31 March 2021.
TOOP was launched in January 2017 as an initiative of about 50 organisations from 20 EU Member States and Associated Countries. The main objective of TOOP was to explore and demonstrate the once-only principle on a cross-border pan-European scale, focusing on reducing the administrative burden of businesses.
TOOP succeeded in creating a reference architecture supporting the organisational, semantic and technical interoperability of national e-gov systems across state borders. This solution was implemented and tested by TOOP partners within different pilot domains.