ISSB, CSRD and BRSR: One Report, Many Regimes?

Why three frameworks exist at all

The differences make more sense once you know where each came from, because each was built to answer a different question.

The ISSB was built for investors. The International Sustainability Standards Board was created by the IFRS Foundation, the body behind the accounting standards used in more than 140 jurisdictions. It issued IFRS S1 and S2 in June 2023 with the explicit purpose of consolidating the fragmented voluntary landscape that companies had complained about for a decade. It absorbed the Climate Disclosure Standards Board and the Value Reporting Foundation, which had itself merged SASB and the Integrated Reporting Framework.

Its question is: what sustainability information does an investor need to assess this company's prospects?

The CSRD was built for society as well as investors. The European Union's regime, delivered through the European Sustainability Reporting Standards, was designed to serve a wider set of users and to support the EU's own policy objectives on climate and human rights.

Its question is: how do sustainability matters affect this company, and how does this company affect the world?

The BRSR was built on Indian responsible-business principles. India's format is structured around the nine principles of the National Guidelines on Responsible Business Conduct, themselves descended from voluntary guidelines issued in 2011 and revised in 2019 to align with the UN Guiding Principles on Business and Human Rights.

Its question is: is this company conducting itself responsibly against a domestically-framed set of principles?

Three different questions produce three different architectures. That is the root of the interoperability problem, and no amount of technical mapping fully dissolves it.

The materiality divide

This is the deepest difference and the one that determines how much duplicated work a company faces.

Financial materiality. The ISSB standards require disclosure of sustainability-related risks and opportunities that could reasonably be expected to affect the entity's prospects. This is sometimes called the outside-in view: the world acting on the company. Information is reportable if it bears on enterprise value.

Double materiality. The CSRD requires both that outside-in assessment and an inside-out one: how the company's activities affect people and the environment, whether or not those effects rebound financially. A company may have to report an environmental impact that costs it nothing.

The BRSR sits between them without matching either. Because it is built on stakeholder-and-impact-oriented principles, it asks a good deal that a purely financial-materiality lens would not require, including community engagement, consumer conduct and policy advocacy. But it does not implement double materiality as a formal assessment discipline in the way the ESRS does.

The practical consequence: a company reporting to ISSB standards has not thereby produced the impact-side content the CSRD wants, and a company reporting under BRSR has not performed the structured double-materiality assessment the ESRS requires.

Where the three genuinely overlap

The convergence is real, and it is concentrated in climate.

All three regimes draw on the TCFD four-pillar architecture: governance, strategy, risk management, and metrics and targets. IFRS S2 incorporates it directly. The ESRS climate standard follows the same logical shape. India's regime absorbed the same thinking through its climate and energy indicators.

The core quantitative metrics are broadly common: greenhouse gas emissions by scope, energy consumption, water, waste, workforce composition and safety. The definitions are not identical, but the underlying data collection is largely the same exercise.

This is why the practical advice in this article is not "give up and file three reports". A very substantial proportion of the underlying data serves all three. The divergence is in framing, materiality assessment, granularity and assurance, not in whether you need to know your Scope 1 emissions.

Where they genuinely differ

Five differences matter operationally.

Materiality, as above. The single largest source of additional work.

Adoption status. The ISSB standards bind nobody by themselves. They apply where a jurisdiction adopts them. On the count, the ISSB Chair stated in May 2026 that 43 or 44 jurisdictions were adopting, against 30 a year earlier, while the IFRS Foundation's own published figure was 36 as at June 2025. The Foundation counts jurisdictions that have adopted and those finalising steps to adopt as a single figure, so the two counts are not measuring the same thing. India is not among them.

Assurance. The CSRD requires assurance across its reporting. India requires assurance or assessment only of the defined BRSR Core subset, the choice between the two having been introduced by SEBI's circular of 28 March 2025 and the corresponding LODR amendment. ISSB itself does not mandate assurance; the adopting jurisdiction decides.

Value chain and Scope 3. The regimes differ in how deep they push into the supply chain. India's value chain disclosure was made fully voluntary by the same circular of 28 March 2025 and applies to the top 250 listed entities where undertaken.

Sector granularity. IFRS S1 points to SASB industry-based metrics as a source of industry-specific disclosure. The ESRS has its own sector approach. The BRSR is largely sector-agnostic.

The interoperability work that has actually been done

Two developments have narrowed the gap, and a company planning its reporting architecture should know about both.

The Interoperability Guidance. On 2 May 2024 the IFRS Foundation and EFRAG jointly published the Interoperability Guidance illustrating the alignment between the ISSB standards and the ESRS, explicitly designed to reduce complexity, fragmentation and duplication for companies applying both. It does not merge the regimes, but it maps them, which converts an open-ended problem into a documented reconciliation.

The ESRS simplification. EFRAG has produced revised standards that cut mandatory datapoints by 61 per cent and remove all voluntary datapoints, and reframe the ESRS as a fair presentation framework similar in character to the ISSB approach. Definitions, concepts and language have been harmonised with IFRS S1 and S2.

The European Commission has since adopted the delegated act revising the original ESRS: C(2026) 5010 final of 3 July 2026, amending Delegated Regulation (EU) 2023/2772, applying to financial years beginning on or after 1 January 2027. It was not yet published in the Official Journal at this review date, so it should be cited by its C-number rather than by an (EU) 2026 number. The applicability date is no longer open. Anyone planning against the revised standards should work from the adopted text rather than from EFRAG's draft.

The direction is unmistakable: the ESRS is moving toward the ISSB, not away from it.

What this means for an Indian company

Four scenarios, in ascending order of complexity.

You file only a BRSR. Most of the top 1,000 listed Indian entities are here. No interoperability problem arises. Build good data and move on.

You file a BRSR and face investor pressure for ISSB-aligned disclosure. Common for companies with significant foreign institutional holding. Your BRSR does not satisfy the request, because India has not adopted the standards. You will need to produce ISSB-aligned climate disclosure separately, though largely from the same data.

You file a BRSR and are caught by the CSRD. Far fewer companies now, since Omnibus I narrowed the third-country thresholds. If you are caught, the double-materiality assessment is genuine additional work that no amount of BRSR preparation substitutes for.

You are a large Indian group with European subsidiaries and global investors. All three are live. This is where the "build once, map many" discipline pays for itself.

The practical answer: build once, map many

The mistake that costs the most is building a separate data system for each regime. Companies that have done this discover that their BRSR emissions figure and their investor-report emissions figure differ, and cannot explain why.

The better approach has four elements.

Collect at the highest common granularity. Where regimes differ on how finely something must be broken down, collect to the finest requirement. Aggregating down is trivial; disaggregating after the fact is impossible.

Document the basis of preparation once, per metric. What is measured, over what boundary, using what method, from what source, with what conversion factors and what estimation. Every regime asks a version of this question, and a single documented basis answers all of them.

Maintain a mapping table, not parallel reports. One dataset, with a mapping showing which field satisfies which requirement under which framework. The Interoperability Guidance is the reference point for the ISSB and ESRS legs.

Build to the strictest assurance standard you will face. If BRSR Core assurance applies to you and CSRD assurance may, build the controls for the harder one. Data that survives reasonable assurance survives everything below it.

The underlying principle is that the regimes differ in what they ask you to say, far more than in what they require you to know. Build the knowing once.

What would change this picture

Three developments worth watching, because any of them would materially reduce the duplication.

India-ISSB alignment. Widely anticipated and not enacted. If India adopts or aligns with IFRS S1 and S2, the largest single gap for Indian multinationals closes.

The revised ESRS delegated act. If the 61 per cent datapoint reduction and the fair-presentation reframing survive into the final instrument, the ESRS and ISSB legs converge substantially.

Whether India re-tightens value chain reporting. Currently voluntary. If it becomes mandatory, the BRSR moves closer to the CSRD's supply chain expectations.

Frequently asked questions

Will our BRSR satisfy the ISSB standards? No. India has not formally adopted IFRS S1 and S2, so a BRSR is not automatically an ISSB-compliant report. The underlying data overlaps substantially, but the report itself does not qualify.

What is the main difference between the ISSB standards and the CSRD? Materiality. The ISSB requires disclosure of sustainability matters affecting the company's own prospects, which is financial materiality. The CSRD additionally requires disclosure of the company's impacts on people and the environment, which is double materiality.

Where does the BRSR sit on materiality? Closer to the double-materiality end, because it is built on stakeholder-and-impact-oriented principles, but it does not implement double materiality as a formal assessment discipline in the way the ESRS does.

Do the three frameworks share anything? Yes. All draw on the TCFD four-pillar architecture of governance, strategy, risk management, and metrics and targets, and the core quantitative metrics on emissions, energy, water, waste and workforce are broadly common.

How many jurisdictions have adopted the ISSB standards? It depends which count and whose, and the corpus states all three. The IFRS Foundation's April 2026 position was roughly 28 adopting on a voluntary or mandatory basis with about a dozen more planning to; its own published figure was 36 as at June 2025 on a wider basis that includes jurisdictions still finalising steps; and the ISSB Chair said in May 2026 that 43 or 44 were adopting. The three rest on different bases and should not be compared or added. India is not among the adopters on any of them.

Is there official guidance on using ISSB and ESRS together? Yes. The IFRS Foundation and EFRAG jointly published Interoperability Guidance on 2 May 2024, mapping the alignment between the two and designed to reduce duplication.

Is the ESRS being simplified? Yes. EFRAG's revised standards cut mandatory datapoints by 61 per cent, remove all voluntary datapoints and reframe the ESRS as a fair presentation framework closer to the ISSB approach. The European Commission has since adopted the delegated act revising the original ESRS, C(2026) 5010 final of 3 July 2026, amending Delegated Regulation (EU) 2023/2772.

Can we file one report for all three regimes? Not as a single document today. You can, and should, build one dataset that serves all three, with a mapping showing which field satisfies which requirement.

Which should we build towards if we can only build for one? The ISSB baseline, because it is the framework converging jurisdictions are adopting and because the ESRS is moving toward it. Add the BRSR Core specifics that Indian filing requires.