What are ISSB S1 and S2 standards

Sustainability reporting used to be a patchwork. A company could publish a glossy ESG report, a TCFD statement, a SASB index, and a CDP questionnaire, and investors still could not compare two firms side by side. IFRS S1 and S2 are the International Sustainability Standards Board's attempt to end that mess with a single global baseline, built on the bones of the frameworks it absorbed.

More than 30 jurisdictions representing over half of global GDP have taken steps toward the ISSB standards, and rules mandating their use became effective at the start of 2026 in places like Chile, Qatar, and Mexico. If your company sells, borrows, or lists across borders, the question is no longer whether these standards apply to you, but when.

Where the standards came from

The IFRS Foundation's sustainability arm

The ISSB was announced on 3 November 2021 at COP26 in Glasgow, created by the trustees of the IFRS Foundation, the same body that oversees the IASB and its accounting standards used in more than 140 jurisdictions. The logic was blunt: investors had financial statements they could compare across borders, but no equivalent for sustainability data. The ISSB was built to fix that gap and sit alongside the IASB under the same trustees.

It took roughly 19 months from that announcement to the finalised standards. IFRS S1 and IFRS S2 were issued in June 2023, both effective for annual reporting periods beginning on or after 1 January 2024.

From TCFD, SASB, CDSB to one baseline

The ISSB did not start from scratch. It consolidated the Climate Disclosure Standards Board and the Value Reporting Foundation, which housed the Integrated Reporting Framework and the SASB Standards, into the IFRS Foundation by mid-2022. It then built S2 on the four-pillar architecture of the TCFD recommendations and folded SASB's industry-specific metrics into the climate standard. In 2023, the TCFD's monitoring role was formally handed over to the ISSB.

That inheritance matters. A company already reporting against TCFD will recognise the bones of S2. A company already using SASB metrics will find them referenced directly.

IFRS S1 in plain terms

What S1 actually requires

S1 is the general standard. It sets out how a company reports on any sustainability-related risk or opportunity that could reasonably be expected to affect its cash flows, access to finance, or cost of capital over the short, medium, or long term. It is deliberately broad. Environmental, social, and governance topics all sit under it. S1 also prescribes the content, presentation, and location of disclosures so they line up with the related financial statements and cover the same reporting entity and the same reporting period.

The four-pillar structure

S1 organises disclosures around four pillars borrowed from the TCFD architecture: governance, strategy, risk management, and metrics and targets. A company must describe the board and management processes used to oversee sustainability issues, the strategy for managing them, the processes for identifying and prioritising risks and opportunities, and the metrics and progress against any targets it has set or is legally required to meet.

Materiality, reporting timing, and location

S1 uses a single-materiality lens. Information is material if omitting, misstating, or obscuring it could reasonably be expected to influence the decisions of primary users of general purpose financial reports. Disclosures must be published at the same time as the related financial statements, with a first-year exemption that allows a company to publish them alongside its next half-year interim report instead. They can sit inside management commentary, a strategic report, or an equivalent section, as long as they are clearly identifiable.

IFRS S2 in plain terms

Climate risks and opportunities in scope

S2 narrows the aperture to climate. It covers climate-related physical risks, such as flooding, heat, and water stress, and climate-related transition risks tied to policy, technology, and market shifts. It also covers the opportunities a company may be positioned to capture, from cleaner products to new service lines. Anything climate-related that could reasonably be expected to affect the company's prospects is in scope. Anything that could not is out.

Scope 1, 2, and 3 emissions

Here is where S2 bites hardest. Companies must disclose Scope 1, Scope 2, and Scope 3 greenhouse gas emissions measured in accordance with the Greenhouse Gas Protocol, unless they are required by a jurisdictional authority or an exchange to use a different method. Scope 3 is the tough one because it covers the value chain, upstream and downstream, and the data rarely sits in a company's own systems.

The ISSB built in reliefs. In the first year of applying S2, a company does not have to disclose Scope 3 emissions. It can also keep using its existing measurement method for Scope 1 and 2 in that first year rather than switching to the GHG Protocol immediately. Scope 3 disclosure becomes mandatory from year two.

Industry-based metrics and scenario analysis

S2 pulls in industry-based disclosure requirements derived from the SASB Standards, so an oil and gas producer answers different questions than a software firm. It also requires climate resilience analysis using scenario analysis appropriate to the company's circumstances, along with disclosure of internal carbon prices used in decision-making, capital deployed to climate risks and opportunities, and whether executive pay is linked to climate targets.

How S1 and S2 fit together

Why S2 is read through S1

S1 is the operating manual and S2 is a chapter inside it. A company applying S2 is also applying the general presentation, materiality, and governance rules in S1. You cannot pick one without the other in practice. Early application of either standard is allowed only if both are applied together.

Transition reliefs in the first year

In the first annual reporting period, a company may choose to report only on climate-related information under S2 and defer the broader S1 topics until year two. It also gets the Scope 3 exemption, does not need to provide comparative information for the first year, and can publish sustainability disclosures later than the financial statements. These reliefs were added to give preparers time to build systems without watering down the end state.

Who has to comply

Jurisdictions that have adopted

The ISSB itself does not mandate anything. Adoption happens country by country. The UK has endorsed ISSB-aligned UK Sustainability Reporting Standards with a phased rollout starting with the largest listed companies. Australia made AASB S1 and S2 mandatory for its largest group of reporters from FY 2024-25, with smaller tiers phased in through FY 2027-28. Japan's SSBJ has finalised ISSB-aligned standards with the first mandatory wave landing in FY 2027 for companies with market capitalisation above JPY 3 trillion. Hong Kong, Singapore, and Malaysia have mandated ISSB-aligned climate disclosures for listed companies from FY 2025. Nigeria adopted IFRS S1 and S2 directly as an early mover. Brazil's CVM has a phased mandate starting FY 2026. Chile, Qatar, and Mexico activated their rules at the start of 2026.

The EU's parallel track and interoperability

The European Union went its own way with the European Sustainability Reporting Standards under the Corporate Sustainability Reporting Directive. ESRS uses a double materiality test, meaning companies report on both how sustainability issues affect them and how they affect people and the environment. ISSB uses single materiality focused on financial impact to the company. EFRAG and the ISSB have published interoperability guidance so a company reporting under one can largely satisfy the other for the climate pillar, but the two frameworks are not identical and probably never will be. In the United States, there is no federal mandate. California has state-level climate disclosure laws, and large multinationals often end up captured by foreign mandates anyway.

What to do now

Data gaps companies hit first

The first wall companies run into is Scope 3. Suppliers do not report consistently, categorisation is judgemental, and methodology choices drive wildly different totals. The second wall is governance evidence. Boards often do discuss climate, but the paper trail showing how, when, and with what data is thin. The third is scenario analysis that passes external scrutiny. A qualitative paragraph does not count.

A practical sequence for the first reporting cycle

Start by mapping which jurisdiction's version of the standards applies to your entities and which reporting period triggers first. Then do a gap assessment against the four pillars, climate first, given the transition relief allows a climate-only year one. Lock down governance artefacts - board minutes, committee charters, delegation paths - because these are cheap wins that auditors will ask about. Build Scope 1 and 2 data with a clean boundary and pick a measurement method you can defend. Treat year one as the rehearsal for Scope 3, not the exemption from thinking about it. Decide early whether you will seek assurance, and at what level, because that choice drives your documentation standard more than anything else.

Ten years ago, a climate disclosure was a brand exercise. With S1 and S2 written into listing rules from Sydney to Santiago, it is an audit item. The companies that treat year one as a rehearsal, not a box-tick, will spend year three arguing about strategy instead of spreadsheets.