By default, Horizon Europe projects are required to ensure open access to research data under the principle of “as open as possible, as closed as necessary” and must deposit the following in a trusted research data repository:

1. All data needed to validate the results presented in scientific publications, including the metadata describing the deposited research data (the so-called “underlying data”). These data must be made openly available as soon as possible, and at the latest at the time of publication, unless legitimate exceptions apply.
2. Other data, including curated and/or raw data, together with the associated metadata, as defined in the Data Management Plan (DMP) and according to the project’s strategy for FAIR data management. This includes respecting any timelines, access conditions, and justifications for restrictions outlined in the DMP.
3. Information about the tools, software, algorithms, and protocols needed to validate and reproduce the results. Where possible, beneficiaries are expected to provide these tools themselves or ensure access to them, in line with open science practices and reproducibility requirements.

The legal obligations for participating projects are defined in Article 17 of the Horizon Europe Model Grant Agreement, which establishes requirements for open science, including research data management, FAIR data, and open access to research outputs. Provisions for exceptions, opt-outs, and justified restrictions are also specified within the Grant Agreement and accompanying guidance.

The EC requires data to be deposited in ‘metadata-ready’ and ‘trusted’ repositories.

Researchers, information managers and other stakeholders can rely on a framework of internationally recognised certification standards for digital repositories in order to assess and improve the quality of their work processes and management systems. “Trustworthy Digital Repository” (TDR) is a term often used in this respect, referring to repositories that ensure long-term preservation, accessibility, and reuse of research outputs.

In the European Framework for audit and certification of digital repositories three certification instruments, with increasing degrees of complexity and depth, are available:

• CoreTrustSeal (CTS): this is based on Data Seal of Approval (DSA) and World Data System (WDS) and represents the most widely adopted certification, focusing on core requirements such as data integrity, accessibility, and sustainability. All digital repositories that have one or more of these certifications are listed athttps://www.coretrustseal.org/why-certification/certified-repositories/"> https://www.coretrustseal.org/why-certification/certified-repositories/
• Nestor Seal: verification according to DIN 31644
• ISO 16363 certification

The assessments vary in intensity from a peer review of completed documentation (self-assessment) to a prepared on-site visit by an external audit team. These instruments are used worldwide. Data sponsors, producers and re-users may trust any managing body that has been certified according to one of the above standards.

There are also data repositories with a long standing and solid user base, like Zenodo; you’ll find other examples in OpenDOAR, the directory of Open Access repositories. 

However, many of these repositories do not yet match the European Commission’s set of FAIR standards that metadata should follow. Not all ‘trusted repositories’ are fully ready for Horizon Europe compliance.

Currently, only 5 trusted repositories are ‘ready’ for compliance (HAL, AUSSDA, <intR>²Dok, DANS Data Station Archaeology, Zenodo). However, it is expected that other repositories will become ‘close to essential’ in the near future. 

Did you know?
In doubt, deposit in the EU Open Research Repository in Zenodo (for compliance), and also in a subject-specific and/or institutional repository (to improve visibility and discoverability, and get better community engagement and networking).

How to achieve this?
Read the “Background” section below (What are these repository certifications based on?) when you want to know how the requirements for certification support the FAIR data principles.

Did you know?
A trustworthy repository is designed not only to store data but to guarantee their long-term usability, integrity, and accessibility, supporting reproducibility and reuse of research outputs (European Commission, Horizon Europe Model Grant Agreement, Article 17; CoreTrustSeal documentation).

During the project, you are expected to manage your data, metadata and documentation in line with the FAIR principles (Findable, Accessible, Interoperable, Reusable) and in accordance with the standards and good practices in your discipline.This includes ensuring that metadata are rich, accurate, and use community standards, as their quality directly affects data reuse.

Before the deadlines mentioned above, you deposit this package in a trusted repository that supports FAIR data and long-term preservation. Remember to also deposit data that cannot be made open (e.g. sensitive or restricted data), ensuring that appropriate access conditions and justifications are provided.

Once the data are published you refer to them with a so-called persistent identifier or PID, like a DOI or a URN:NBN. PIDs provide a stable and unique reference to your data, ensuring they remain findable, accessible, and citable over time, and preventing issues such as link rot and content drift. This enables the research funder and potential users of your data to find and later cite your data.

Watch this video by Research Data Netherlands when you want to know more about PIDs and data citation.

Watch this video by Research Data Netherlands when you want to know more about PIDs and data citation.

Attaching a usage licence to your data tells others what they can or cannot do with the data. OpenAIRE recommends to use the Creative Commons CC0 waiver or the CC-BY licence licence for open access to data. Providing a clear and accessible licence is a key requirement for making data reusable under the FAIR principles. Creative Commons offers more restrictive licences for data if needed, and the EUDAT License Selector helps you to select software licences as well.

The good news is that trustworthy repositories can help you with PIDs and licences by assigning identifiers, supporting metadata standards, enabling access control, and guiding you in selecting appropriate licences.

Did you know?
The quality of metadata determines whether your data can be reused.
Rich and standardised metadata enable both humans and machines to find, understand, and reuse datasets effectively.

Did you know?
Persistent Identifiers (PIDs) are essential for long-term access and trust.
They ensure that research outputs remain uniquely identifiable and accessible over time, avoiding link rot and content drift.

Did you know?
Even restricted data should be deposited in repositories.Repositories allow you to apply access controls (e.g. restricted, embargoed, or controlled access) while still making metadata publicly available.

(FCT, n.d.; PATTERN Project, 2024, https://doi.org/10.5281/zenodo.15310506)

The general steps for finding a data repository are:

• use a disciplinary repository if there is one;
• alternatively, use the institutional repository, if you have one that supports long-term preservation, FAIR data practices, and institutional policies;
• use the catch-all repository Zenodo, maintained by CERN;
• or search in a global registry - re3data or FAIRsharing - for a fitting repository (they provide several filtering options and information on standards, policies, and certifications).

It’s not easy to evaluate the quality of repositories, because this is influenced by many external factors, starting with the mission of the repository. For instance, does it explicitly aim for long-term preservation - with the appropriate expertise and budget - or not? Is it dedicated to a specific research community and familiar with their data formats, or is it generic? 

Does it support FAIR principles through metadata standards, persistent identifiers, and clear access conditions?

However, if you focus on repositories that are certified as being trustworthy, you simplify your selection process. So, if you don’t have a disciplinary repository, and use the re3data portal for your search, we recommend that you filter on “Certificate” and look for the red icon (which identifies the repository as having a certificate). Searching in FAIRsharing you can look to the section "Certifications and community badges" to find if the repository is certified. 

Certification (e.g. CoreTrustSeal) indicates that the repository meets recognised standards for data integrity, accessibility, and long-term preservation.

Did you know? Disciplinary repositories are often the best choice.
They are tailored to specific research communities and support domain-specific metadata standards and formats, improving interoperability and reuse.
(PATTERN Project, 2024 – https://doi.org/10.5281/zenodo.15310506)

Did you know? Certification helps identify trustworthy repositories quickly.
Frameworks like CoreTrustSeal assess repositories against requirements such as data integrity, preservation, and accessibility, making them more reliable choices.
(CoreTrustSeal, 2023 – https://www.coretrustseal.org/why-certification/requirements)

Did you know? Trustworthy Digital Repositories are key for long-term data preservation in EOSC.
They ensure that research data remain usable, accessible, and valuable over time, supporting reproducibility and reuse.
(EOSC LTDP Task Force, 2022 – https://doi.org/10.5281/zenodo.7034315)

Institutions and repositories may offer practical guidance on metadata creation, sustainable file formats, the management of sensitive data, and the choice of appropriate usage licences. They often support researchers in applying discipline-relevant metadata standards and controlled vocabularies, helping ensure that data are well described, understandable, and reusable over time. Metadata are essential for making data findable, interpretable, and meaningful both for humans and for machines.

You may notice that so-called ‘trustworthy’ repositories are sometimes more demanding than non-certified repositories. This is because they work to support the long-term preservation, accessibility, and reusability of data, and this requires active collaboration from depositors. For example, repositories may ask researchers to provide preferred or open file formats, richer metadata, documentation, and clear information on access and reuse conditions. Such requirements are not barriers; they are part of ensuring that data remain usable and meaningful in the long term.

Most repositories also provide persistent identifiers (PIDs), so it is useful to contact them early in the research process to plan data management in a way that supports FAIR implementation and meets repository or funder expectations. Guidance such as How to FAIR and A FAIRy tale emphasises that planning ahead helps researchers make better choices about documentation, formats, access, and reuse conditions.

Repositories also support the management of sensitive data by enabling different levels of access, such as restricted, embargoed, or controlled access, while offering guidance on anonymisation, ethical considerations, and legal compliance. In this way, data that cannot be fully open may still be shared responsibly, with metadata remaining openly available so that others can discover the existence of the dataset and understand under which conditions it may be accessed. This approach is strongly reflected in responsible data guidance and research data management practice.

Read more about this in section below “What are these repository certifications based on?”.

Did you know? Metadata quality is critical for reuse.
IRepositories often require rich, accurate, and standardised metadata, as this directly determines whether datasets can be found, understood, and reused.

Did you know? Open formats support long-term preservation.
Repositories encourage the use of non-proprietary or well-documented file formats to ensure data remain accessible and usable over time.This is a key part of good research data management and long-term stewardship.Did you know?

Did you know? Sensitive data can still be shared responsibly.
Repositories allow different access levels (e.g. restricted, embargoed, controlled access) while ensuring compliance with ethical and legal requirements.

Did you know? Repositories actively support licensing decisions.
They help researchers apply clear and standardised licences (e.g. Creative Commons), which are essential for enabling reuse under the FAIR principles.

Many repositories don’t charge you for depositing data with them (nor for downloading data, for that matter). The costs of making your data available via a repository are then limited to the time you may need to prepare the data for archiving, so it’s recommended to plan this in a timely fashion. However, some repositories (especially specialised or large-scale infrastructures) may charge fees for storage, curation, or long-term preservation services.

Under Horizon Europe, costs related to research data management (RDM) and open access to research data are eligible for reimbursement, provided they are justified and included in the project budget. This includes costs for data preparation, curation, storage, and, where applicable, repository fees.

These costs must:

• be foreseen and justified in the project proposal and budget;
• be incurred during the project duration;
• comply with the conditions set in the Horizon Europe Model Grant Agreement (Article 6 – Eligible costs, and Article 17 – Open Science). 

Did you know? Data management costs go beyond repository fees.
They may include time spent on data cleaning, documentation, metadata creation, licensing, and compliance with FAIR principles, hiring of data stewards, etc.
(OpenAIRE; PATTERN Project, 2024 –https://doi.org/10.5281/zenodo.15310506)

Did you know? Planning RDM costs early is essential.
Including data management activities in your proposal ensures that resources are available for proper data stewardship throughout the project lifecycle.
(European Commission, Horizon Europe Programme Guide)

Did you know? Investing in FAIR data increases research impact.
Well-managed and accessible data can lead to greater visibility, reuse, and citation of research outputs.
(OpenAIRE; PATTERN Project, 2024 –https://doi.org/10.5281/zenodo.15310506)

(Background information)

Here are the main requirements that a repository with a CoreTrustSeal complies with Italics mark clear connections with the FAIRness of data. These requirements align closely with the FAIR principles and support the European Commission’s objective of ensuring “FAIR data in trustworthy repositories.” Remember: the Commission wants FAIR data in trustworthy repositories. Researchers and trustworthy repositories are partners in Open and FAIR data.

Requirement 1 (R1): The repository maintains all applicable licenses covering data access and use and monitors compliance. This ensures clarity on reuse conditions and supports the Reusability (R) principle of FAIR.

Requirement 2 (R2): The repository has a continuity plan to ensure ongoing access to and preservation of its holdings. This guarantees long-term accessibility and sustainability of research data.

Requirement 3 (R3):The repository ensures, to the extent possible, that data are created, curated, accessed, and used in compliance with disciplinary and ethical norms. This includes compliance with legal and ethical frameworks such as GDPR and community standards.

Requirement 4 (R4):The repository guarantees the integrity and authenticity of the data. This ensures that data remain reliable and trustworthy over time.

Requirement 5 (R5):The repository accepts data and metadata based on defined criteria to ensure the relevance and understandability for data users. This includes requirements for rich, structured metadata and proper documentation.

Requirement 6 (R6):The repository assumes responsibility for the long-term preservation and manages this function in a planned and documented way. This reflects the core role of repositories in ensuring long-term usability of data.

Requirement 7 (R7):The repository has appropriate expertise to address technical data and metadata quality and ensures that sufficient information is available for end users to make quality-related evaluations. This highlights the role of repositories in supporting data quality, metadata standards, and user guidance.

Requirement 8 (R8):The repository enables users to discover the data and refer to them in a persistent way through proper citation. This is typically achieved through the use of Persistent Identifiers (PIDs), supporting the Findability (F) principle.

Requirement 9 (R9):The repository enables reuse of the data over time, ensuring that appropriate metadata are available to support the understanding and use of the data. This directly supports the Reusability (R) principle through licensing, documentation, and metadata.

Did you know? CoreTrustSeal includes 16 core requirements for trustworthy repositories.
These cover areas such as data integrity, access, preservation, governance, and reuse, ensuring alignment with FAIR principles.
(CoreTrustSeal, 2023 – https://www.coretrustseal.org/why-certification/requirements/)

Did you know? Certification requirements are closely aligned with FAIR principles.
They ensure that data are findable (through PIDs and metadata), accessible (via clear policies), interoperable (through standards), and reusable (through licences and documentation).
(Wilkinson et al., 2016 – https://doi.org/10.1038/sdata.2016.18; CoreTrustSeal, 2023)

Did you know? Trustworthy Digital Repositories are essential for EOSC.
They provide the infrastructure needed to ensure that research data remain accessible, usable, and valuable over time, supporting reproducibility and reuse.
(EOSC LTDP Task Force, 2022 – https://doi.org/10.5281/zenodo.7034315)

Factsheet:

• Open Research Data Pilot in Horizon 2020 

 Information from the European Commission:

• European Commission, Horizon Europe Programme Guide, 2023

Guides:

• Zenodo - A universal repository for all your research outcomes

OpenAIRE Validation Service
For data source managers OpenAIRE provides a Validator tool (accessible through OpenAIRE PROVIDE) to check if a given repository complies with the OpenAIRE guidelines.

View our webinar recordings:

• Horizon Europe Programme Guide (Open Science & FAIR data)
• Wilkinson, M., Dumontier, M., Aalbersberg, I. et al. The FAIR Guiding Principles for scientific data management and stewardship. Sci Data 3, 160018 (2016). https://doi.org/10.1038/sdata.2016.18
• CoreTrustSeal (official requirements & certified repositories)
  https://www.coretrustseal.org/why-certification/requirements/
  https://www.coretrustseal.org/why-certification/certified-repositories/
• Donaldson, D.R., Russell, S.V. (2023). Trustworthy Digital Repository Certification: A Longitudinal Study. In: Sserwanga, I., et al. Information for a Better World: Normality, Virtuality, Physicality, Inclusivity. iConference 2023. Lecture Notes in Computer Science, vol 13972. Springer, Cham. https://doi.org/10.1007/978-3-031-28032-0_42">https://doi.org/10.1007/978-3-031-28032-0_42
• EOSC Task Force on Long-Term Data Preservation. (2022). How a European network of FAIR-enabling Trustworthy Data Repositories can align to the vision of EOSC. Zenodo. https://doi.org/10.5281/zenodo.7034315
• PATTERN Project Consortium. (2024). PATTERN training on intermediate level FAIR research data management (RDM). Zenodo. https://doi.org/10.5281/zenodo.15316306
• Thorpe, D. E., van den Berk, M., van Horik, R., Brinkman, L., Macan, B., Žugaj, M., & Jurković, S. (2026). FAIR Research Data Management Training Materials Ready for Reuse. 20th International Digital Curation Conference (IDCC26), Zagreb, Croatia. Zenodo. https://doi.org/10.5281/zenodo.18834884
• UNESCO. (2023). Practical guide to sustainable research data. United Nations Educational, Scientific and Cultural Organization. https://www.unesco.org/en/open-science/practical-guide-sustainable-research-data

Last update: March 2026