Schmidt, CarstenKrimmer, RobertJ. Lampoltshammer, ThomasRoßnagel, HeikoSchunck, Christian H.Mödersheim, Sebastian2021-05-202021-05-202021978-3-88579-706-7https://dl.gi.de/handle/20.500.12116/36498The Single Digital Gateway Regulation (SDGR) and the underlying Once-Only Principle (OOP) outlining that businesses and citizens in contact with public administrations have to provide data only once. Until now many MS and associated countries have started to implement the OOP at national level, but the cross-border implementation is still work in progress. The SDGR as one of the cornerstones of the Digital Single Market for the EU will bust this development. The authors of this paper present the development related to the SDGR and OOP in Europe. They will also show the interconnections and interdependencies between the OOP and electronic identities (eID). The paper gives an overview based on the findings of the EU-funded “The Once-Only Principle Project (TOOP)” and mobile Cross-Border Government Services for Europe (mGov4EU).enOnce-Only PrincipleSingle Digital GatewaySDGRDSMmGov4EUTOOPeIDeIDASText/Conference Paper1617-5468