Most listed companies have a well-worn ESEF routine by now. Finance prepares the annual financial report as one electronic file and tags the IFRS statements. The auditor then reviews the tags, and the report goes out on time. Few people outside the reporting team give it much thought.
CSRD is pulling the ESG team into a process that finance used to run alone. The sustainability statement now sits in that same annual report and goes through the same review season. Eventually, it will need tags as well. For finance teams, CSRD assurance means sustainability figures will face the same scrutiny their own numbers already receive.
This guide covers where ESEF and CSRD overlap and what Omnibus I has and hasn’t changed. It also shows how to prepare now so your first assurance review goes smoothly.
How ESEF and CSRD Divide the Work
The easiest way to separate the two is to ask what each one is responsible for.
ESEF handles presentation. Delegated Regulation (EU) 2019/815 sets out the ESEF rules. Companies with securities listed on an EU regulated market must publish their annual financial report as an XHTML file.
Inside that file, they tag the IFRS statements using inline XBRL. The aim is that software can read each key figure without anyone retyping it.
CSRD handles substance. It determines:
- Which companies report;
- The standards they report against (the ESRS, together with the EU Taxonomy Article 8 disclosures);
- The section of the management report where the disclosures belong;
- The requirement for independent assurance.
Since the Omnibus amendments, it reaches companies employing more than 1,000 people with net turnover above €450 million.
So one rulebook governs the container and the other governs much of what goes into it. A large listed company has to satisfy both in a single document.
Which Companies Feel The Overlap
The scope tests work differently. Being listed is what brings a company into ESEF; being large is what brings it into CSRD. That produces very different starting positions.
Large listed groups answer to both regimes and feel the convergence most directly. Smaller listed companies below the CSRD thresholds carry on with ESEF as before.
Large companies that aren’t listed will find the change hardest, because CSRD will be their first time using XBRL tagging. A company that belongs to a larger group may not need its own CSRD report if its parent’s sustainability statement already covers it.
Five Overlaps Sustainability Teams Should Plan Around
1. The same publication
The sustainability statement is part of the management report, and the management report must follow the electronic reporting format. Financial and sustainability disclosures are therefore released together in one annual report.
2. The same tagging language
Financial statements are tagged using the ESEF taxonomy. For sustainability statements, the ESRS XBRL taxonomy and an Article 8 taxonomy are being built to work within the ESEF framework. Teams that already know XBRL will recognise the mechanics and validation rules. What they’ll need to learn is a new vocabulary of reporting concepts.
3. The same review season
From the first reporting year, every in-scope company must obtain limited assurance on its sustainability statement. That work happens during the annual reporting window that already holds the financial audit. CSRD assurance also extends to compliance with the digital mark-up requirements, broadly the way auditors already treat ESEF tags on the financial statements.
4. The same access point
The European Single Access Point (ESAP) will hold both financial and sustainability information. ESMA has until 10 July 2027 to set it up, and core data under the Accounting Directive and CSRD becomes accessible from January 2028. Companies will submit through designated collection bodies, typically Officially Appointed Mechanisms or National Competent Authorities.
5. The same figures
Some figures appear twice: once in the financial statements and again in the sustainability statement. These include revenue, headcount, capex, opex and Taxonomy-aligned turnover.Someone flicking through a PDF might miss a discrepancy between the two. Once both sit in one tagged file, auditors and the software reading the data are far more likely to spot it.
Omnibus I: What’s On Hold And What Still Applies
Under Omnibus I, sustainability tagging has been paused. Companies don’t have to tag their sustainability disclosures yet. That requirement only starts once the EU updates the ESEF rules to include them. There’s no confirmed start date.
The logic is about timing. With the ESRS revised, the tagging rules needed revising too. Asking companies to tag against the earlier standards would simply have created rework.
Meanwhile, the technical groundwork continues. On 17 September 2026, EFRAG released a draft ESRS XBRL taxonomy based on the revised standards. The consultation closes on 11 November 2026. EFRAG then plans to send the final version to ESMA and the European Commission by the end of the year.
Several obligations are unaffected:
- The sustainability statement still has to appear in the management report.
- Limited assurance still applies. The EU now has until 1 July 2027 to adopt assurance standards.
- ESAP is on its original schedule.
- Development of the tagging framework is still moving.
Tagging is postponed rather than abandoned. Companies have gained time, and the sensible use of that time is preparation.
Preparing For CSRD Assurance While Tagging Waits
Two regulations sit behind it, but for a large listed company the end state is one report, one assurance cycle and one access point.
Bring finance controls to sustainability data
Finance teams already know how to keep ESEF filings reliable. They give each dataset a clear owner, reconcile figures on a fixed schedule, and sign off before anything goes public. Sustainability reporting needs that same structure.
Materiality decisions stay with the sustainability team. Finance’s contribution is making sure every reported number can stand up to questioning. Assurers need both.
Questions your assurer is likely to ask
Once the engagement begins, expect questions along these lines. Where does this figure come from? Who approved it, and when? Does it agree with the matching number in the financial statements?
If the answers live in spreadsheets and email threads, the review will be slow.If you capture them at source, the review moves quickly.
Why The Pause Rewards Early Movers
Sustainability tagging is on hold until the ESEF Regulation is amended. Limited assurance, however, applies from the first reporting year, and ESAP starts making CSRD data available in January 2028. Companies that put structured, well-governed data in place now will find tagging is just a final layer on top. Companies that hold off will end up rebuilding their data foundations from the ground up.
Five practical steps:
- Align your data with the ESRS data point structure.
- Tie every shared figure back to one governed source.
- Record the audit trail as your team enters the data, not afterwards.
- Hold sustainability data to the same controls you use for ESEF.
- Run finance and sustainability through a single workflow.
How IRIS CARBON Helps
IRIS CARBON brings ESG data collection, emissions calculation, materiality assessment and digital reporting together in one governed workflow. We built it on IRIS’s experience in XBRL and ESEF reporting. With it, you get a structured, traceable sustainability statement that’s ready for CSRD assurance before tagging becomes mandatory.
