Become an expert on the once-only principle!

The once-only principle aims at eliminating extensive administrative burdens from citizens. But there are many things that have to be taken into consideration depending on the principle itself. Once-only has a lot to with interoperability and the question, how the data is shared between different public authorities. But what does all of that mean in general? If you are not an expert on once-only yet, all of the different terms and project can be a little confusing. To help you understand, what we are working on, we are providing you with a different number on helpful means.

Our information materials

Knowledge Base of once-only cases and enablers

The knowledge base is a digital platform that describes a broad variety on once-only principle cases from Europe and beyond, like the case of the Austrian child benefit. We have also collected a number of enablers, that means infrastructures that facilitate once-only cases. The cases have been collected by our stakeholder community and can therefore be seen, edited and commented by everyone which is part of our online community. If you are not a member yet, please register here. If you have a new case you want to present, please tell us about it! We are constantly looking for presenters for our workshops who want to share their knowledge regarding once-only. Get in contact with us if you are interested!  


During our analysis we have found a number of outstanding implementations of the once-only principle that could serve as role models for other countries. Therefore, we have had a deeper look at them and described them more detailed on our website. If you are looking for inspiration for once-only implementations in your own country, have a look at our showcases. 

Domains and Roadmap Results

 The five domains for the future OOP scenarios were chosen basing on the “information areas related to citizens” suggested in Article 2(2)(a) of the Single Digital Gateway Regulation. The future once-only principle scenarios in the cross-border context describe how future interactions between governments and the corresponding stakeholders could look like, which tools, standards, and technologies can be used to share and reuse data, and further important aspects derived from the present-day point of view. Have a look at five different future OOP scenarios developed by our project team.

Roadmap and Recommendations

This section reflects the outcomes reported in Deliverbale 4.2. This deliverable documents the findings of tasks 4.3 and 4.4 that were carried out in work package 4. Task 4.3 aimed at developing a roadmap of future areas of actions to guide policy makers as well as implementers and funding bodies of the once-only principle. The main objective of this roadmap was to spread the maximum potential of the OOP4C vision.


Data provider, data processor or data requestor – you are reading the different terms but have no idea what they mean? Then you should have a look in our glossary. We have collected a lot of relevant terms which are connected to once-only and interoperability in general. If you think there is one missing or a definition is wrong, please write us and we will share your ideas on our website.

Link list

You are still new on the subject of once-only and interoperability in general and want to know more about it? Then have a look at our link list. We have collected a number of research studies and projects that are related to the topic.

Best-Practice Showcase

  • baby and family © Andrew Branch / Stocksnap / CC0 1.0 Birth Registration and Family Allowance (ALF) 1 May 2015 - Ongoing Austria The Birth Registration and Family Allowance (ALF) service provides parents in Austria the opportunity to receive family allowance without any further applications to fill out. Since the 1st of May 2015, parents only need to go to the Civil Registry Office once or the needed information is already send by the hospital. This data is then shared among relevant authorities in order to reduce the… See more
  • smaertphone and medicine © Negative Space / Stocksnap / CC0 1.0 ELGA (Electronic Health Records) 9 Dec 2015 - Ongoing Austria ELGA is an information system that simplifies the process of accessing patients’ health records for citizens and their doctors, as well as other health care professionals at hospitals, care facilities and pharmacies in Austria. The IS has been gradually rolled out since 2015 and allows health care providers to re-use data. Patients do not need to re-enter health data as these can be consulted… See more
  • Flag of Austria © Mikekilo74 / Wikimedia Commons / CC BY-SA 3.0 FinanzOnline (FON) 1 Jan 2003 - Ongoing Austria FinanzOnline facilitates the access to the Austrian tax administration for citizens and businesses as well as for public administrations through an online portal. Since 2003, citizens can file their tax returns electronically without having to reenter data, as this can be automatically transferred from previous years. How does it work? The FinanzOnline portal allows citizens to file their tax… See more
  • Big Ben in London © David Dilbert / Unsplash / CC0 1.0 Tell Us Once (TUO) 1 Jan 2003 - Ongoing United Kingdom The Tell Us Once (TUO) service makes it possible for citizens in the United Kingdom to inform the government just once of a birth or death of a person without having to contact responsible authorities individually. Since 2011, the service is offered by most local authorities on behalf of the UK Department for Work and Pensions (DWP). Public administrations re-use the data provided by the citizen… See more
  • Students working together © StockSnap/ pixabay/ CC0 1.0 Studielink 1 Jan 2013 - Ongoing Netherlands Studielink is a single point of access for students to manage higher education enrolment data in the Netherlands. It allows students to apply to university through one single platform rather than to every university individually. The students’ data has to be entered only once and can be re-used by the institutions involved. The application first went live in 2003 and is used by all potential… See more
  • Refugees Welcome © Netavisen_Sameksistens_dk/ pixabay/ CCO 1.0 Refugee Digitisation System 1 Jan 2016 - Ongoing Germany The Refugee Digitisation System was implemented in February 2016 in response to the approx. 1,1 million refugees who arrived in Germany in 2015. Due to the immense new data influx, authorities had to establish a coherent, uniform system to register and process refugee data. All relevant authorities now have access to a single core data system which is administered by the Federal Office for… See more
  • Filing taxes electronically © FirmBee/ pixabay/ CCO 1.0 Electronic Tax Filing (e-Tax) 1 Jan 2002 - Ongoing Estonia Since 2002, Estonian citizens can file their taxes using automated tax declaration forms with the Republic of Estonia Tax and Customs Board. This system has continously matured over the years to become more once-only: Since 2015, taxpayers can use the one-click tax returns where the data already known and gathered from different registries is displayed to the citizen automatically without having… See more