Luxembourg has implemented once-only by making it a component of their Guichet.lu-One-Stop-Shop. Guichet.lu is a repository of 1500 descriptions of administrative procedures for citizens and businesses and 170 interactive online procedures accessible via the MyGuichet.lu platform. 

Citizens can use MyGuichet.lu to carry out administrative procedures online using authentication and signature mechanisms such as an eID, smartcard, signing stick, or token. The user can complete the procedure online, sign it electronically, attach any necessary supporting documents, and submit it to the responsible public administration via MyGuichet.lu. The authentication and eSignature service is provided by LuxTrust or any other eIDAS compliant certificate (as of September 2018). LuxTrust is recognised as a trust service by ILNAS (the Luxembourg public standards service). This attests LuxTrust’s expertise and compliance with European security norms and standards. LuxTrust is owned by the State and the main commercial banks of the country, including the ones managed through public funds.

The once-only principle has been implemented by the Luxembourgish government in such a manner that, apart from certain exceptions (i.e. fiscal secrecy), the authentic data already contained in the National Register of Natural Persons is used by public administrations. By default, these administrations therefore do not need to ask citizens’ explicit permission to use that data, and citizens do not need to provide evidence that the data in the register is correct (Law of June 25, 2013, Art. 4). Nevertheless the once-only principle is also applied for other registers or databases not covered by the Law of June 25, 2013 but containing other authentic data such as the Cadastre, Cars register, Driving licence, and the VAT balance sheet. Once-only is implemented in three distinct ways: 1. The data is either reused automatically at back office level without any explicit intervention of the citizen, or 2. if explicit consent by the citizen or business is necessary, an administration can ask for that consent in order to retrieve the information without further intervention of the citizen or business (Example: A public administration needs a copy of a citizen's criminal record. The citizen will not have to provide the document itself; the administration can retrieve that information themselves after the consent was given). 3. Citizens or businesses can decide to reuse information themselves that they submitted to MyGuichet.lu for a particular online service. This means that the information is not coming from an authentic source such as a central register for example.    

"This represents a significant gain of efficiency for citizens, businesses and public administrations. Of course, the need to respect the protection of personal data and privacy remains a primary concern, so technical solutions that ensure that users keep control over their personal data (explicit consent, tracking access ...) have been implemented." (https://joinup.ec.europa.eu/document/oop-luxembourg)

Using once-only for digital e-services for citizens and businesses allows administrations to offer their procedures remotely, in a dematerialised way with the possibilty to track progress and data processes more efficiently. This saves time and other resources for public administrations, citizens and businesses. 

For more information: 

• Join-up news (accessed 20.03.2018) 
• Guichet.lu-One-Stop-Shop (accessed 20.03.2018)
• Luxembourgish Law of June 25, 2013