ISSB, IFRS S1 and IFRS S2 explained: the global sustainability disclosure baseline

The International Sustainability Standards Board (ISSB) is trying to make sustainability disclosure comparable enough for investors to use. International Financial Reporting Standard S1 (IFRS S1) and International Financial Reporting Standard S2 (IFRS S2) do not turn sustainability into a moral scorecard. They move material climate and sustainability information closer to financial reporting discipline.

ISSB matters because it changes the centre of gravity in sustainability reporting. For years, companies could publish climate and environmental, social and governance (ESG) information in separate reports, with different frameworks, different boundaries and different levels of evidence. Investors then had to decide which parts were comparable and which parts were polished narrative.

The ISSB is an attempt to reduce that fragmentation. Its first two standards, IFRS S1 and IFRS S2, create a global baseline for sustainability-related financial disclosure. The important phrase is not "sustainability" on its own. It is "financial disclosure".

ISSB standards are built for users of general purpose financial reports, especially investors, lenders and other capital providers. They ask companies to disclose sustainability-related risks and opportunities that could affect cash flows, access to finance, cost of capital or long-term prospects.

In plain English: ISSB asks whether sustainability issues can change the financial story of the business, and whether the company can explain that link with enough evidence for capital-market users.

Quick answer

What changed in 2026

The standards themselves are not new. IFRS S1 and IFRS S2 were issued in 2023 and became effective for annual reporting periods beginning on or after 1 January 2024. The 2026 story is adoption and use: more regulators, investors and companies are moving from asking what ISSB is to asking how it fits into local reporting rules and existing evidence systems.

What ISSB was created to solve

The ISSB was announced by the International Financial Reporting Standards (IFRS) Foundation at COP26 in Glasgow in November 2021. The problem it was built to address was not a lack of sustainability reports. It was a lack of comparable, decision-useful sustainability information for capital markets.

Large companies already had access to many frameworks. They could use the Global Reporting Initiative (GRI), the Task Force on Climate-related Financial Disclosures (TCFD), Sustainability Accounting Standards Board (SASB) Standards, the Climate Disclosure Standards Board (CDSB) framework, internal ESG scorecards, industry guidance and local regulation.

That created a crowded landscape. Some reports were broad and stakeholder-focused. Some were climate-specific. Some focused on financially material industry topics. Some were voluntary. Some were regulatory. The result was that two companies could both claim strong sustainability reporting while giving investors very different types of information.

ISSB tries to create a common baseline. It does not remove every local rule, and it does not replace every sustainability framework. Instead, it gives regulators and companies a shared starting point for sustainability-related financial disclosure.

The investor lens is the key. ISSB is not mainly asking whether a company has a positive social purpose, or whether every environmental impact has been measured. It is asking what sustainability-related risks and opportunities could reasonably affect the company's prospects.

Why IFRS S1 and IFRS S2 are paired

IFRS S1 and IFRS S2 were both issued in June 2023. They are effective for annual reporting periods beginning on or after 1 January 2024, although companies generally need to look at the rules in their own jurisdiction before assuming when, whether or how they apply.

The two standards work together. For the practical timing question, the 2026 sustainability reporting deadlines guide explains how UK Sustainability Reporting Standards (UK SRS), Corporate Sustainability Reporting Directive (CSRD), Sustainability Disclosure Requirements (SDR) and other evidence deadlines sit alongside ISSB aligned disclosure readiness.

IFRS S1 is the general standard. It sets the architecture for sustainability-related financial disclosures. It asks companies to disclose information about sustainability-related risks and opportunities that could affect cash flows, access to finance, cost of capital or prospects over the short, medium or long term.

IFRS S2 is the climate standard. It applies the same financial-disclosure logic to climate-related risks and opportunities. It covers physical risks, transition risks and climate-related opportunities.

A simple way to read the pair is this: IFRS S1 tells a company how to report sustainability-related financial information; IFRS S2 tells it what climate-related information investors need within that structure.

The big idea: sustainability information as financial information

The most useful way to understand ISSB is to imagine a boundary moving. Sustainability information used to sit outside the core financial story of the business. It was often placed in a separate report, owned by a sustainability team and written in a different style from the annual report.

ISSB pulls some of that information closer to financial reporting. It asks companies to explain sustainability-related risks and opportunities in a way that helps capital providers make decisions.

That does not mean every sustainability issue becomes a financial number. It means the company should explain which issues could affect its prospects, how management oversees them, how they interact with strategy, what processes identify and monitor them, and what metrics show performance or exposure.

For example, a food manufacturer may need to explain exposure to water stress, supply-chain disruption, changing regulation and commodity volatility. A property company may need to explain physical climate exposure, insurance availability and retrofit costs. A bank may need to explain financed emissions, transition risk in its loan book and how climate assumptions affect risk management.

The test is not whether the issue is morally important in the abstract. The test is whether it could reasonably affect the business and matter to users of general purpose financial reports.

How IFRS S2 builds on TCFD

IFRS S2 did not arrive from nowhere. It incorporates and builds on the recommendations of the Task Force on Climate-related Financial Disclosures (TCFD).

That is why the familiar four-part structure remains visible:

• Governance: who oversees climate-related risks and opportunities.
• Strategy: how those risks and opportunities affect the business model, strategy, financial planning and resilience.
• Risk management: how climate risks are identified, assessed, prioritised and monitored.
• Metrics and targets: what the company measures, including greenhouse gas emissions and progress against targets.

The difference is that IFRS S2 turns the TCFD architecture into a formal sustainability disclosure standard. It is more specific about the information investors need and it connects climate disclosure to the wider ISSB baseline.

This is why TCFD is still worth understanding, even though the task force completed its work and disbanded in 2023. The TCFD name may become less prominent, but its structure lives on inside IFRS S2, UK Sustainability Reporting Standards (UK SRS) and other climate disclosure regimes.

For the UK climate-disclosure angle, read TCFD explained and UK SRS and IFRS S2 climate disclosures.

ISSB is not the same as CSRD

One of the easiest mistakes is to treat ISSB and the Corporate Sustainability Reporting Directive (CSRD) as different names for the same thing. They are not.

ISSB standards are designed around sustainability-related financial information for capital markets. They focus on information that could affect enterprise value, cash flows, access to finance, cost of capital or prospects.

CSRD is the European Union's corporate sustainability reporting regime. It uses European Sustainability Reporting Standards (ESRS) and double materiality. That means in-scope companies assess both how sustainability issues affect the company financially and how the company affects people and the environment. For the climate-specific reporting layer, read the guide to ESRS E1 climate change.

There is overlap in practice. Climate data, governance processes, risk management, transition plans and emissions evidence can matter under both systems. But the reporting lens is different.

For a broader map, use the sustainability framework map and the ESG reporting frameworks comparison.

What companies need to prepare

Companies should not treat ISSB readiness as a branding exercise. The hard work is evidence, ownership and controls.

A useful starting point is to ask whether sustainability information is managed with anything like the discipline of financial information. Who owns it? Where does the data come from? Which assumptions are documented? How does the company decide what is material? Can finance, risk, legal and sustainability teams explain the same numbers in the same way?

For many companies, the practical preparation work includes:

• mapping sustainability-related risks and opportunities that could affect prospects;
• assigning board and management responsibility;
• connecting sustainability risks to enterprise risk management;
• documenting Scope 1, Scope 2 and material Scope 3 greenhouse gas emissions data;
• linking climate assumptions to strategy, budgets, capital expenditure and transition planning where material;
• building an evidence file for metrics, targets, methodologies and claims;
• checking whether local rules require ISSB-based reporting, voluntary adoption or no direct action yet.

The last point is important. ISSB standards are not a switch that turns on globally on the same day for every company. Jurisdictions decide whether to adopt, adapt or reference them. Some companies may face direct reporting requirements. Others may encounter ISSB aligned questions through investors, lenders, customers, insurers or procurement teams.

California is a useful example of that wider pattern. Our guide to California climate disclosure laws explains how SB 261 can use ISSB Sustainability Disclosure Standards as an equivalent reporting route while SB 253 focuses on emissions data.

That makes ISSB relevant beyond the formal legal boundary. A private supplier may not be directly in scope, but a listed customer or investor may still ask for climate-risk data, emissions evidence or governance information in an ISSB aligned format.

The evidence file behind ISSB reporting

A useful ISSB workstream is not only a disclosure drafting exercise. It is a source-to-report exercise. The company needs to show how sustainability-related financial information moves from operational data, risk owners and assumptions into a report that capital providers can use.

This is where ISSB overlaps with assurance readiness. The standard tells a company what investors need to understand. The control file shows whether the company can stand behind the disclosure.

What good ISSB aligned disclosure looks like

Good disclosure is specific enough to be useful. It identifies the sustainability-related risks and opportunities that matter to the business, explains who oversees them, connects them to strategy and risk management, and uses metrics that can be traced back to evidence.

Weak disclosure often does the opposite. It says sustainability is important, lists broad commitments, repeats net zero language and gives isolated metrics without explaining methods, boundaries, assumptions or financial relevance.

The strongest disclosures usually have three qualities.

First, they are connected. The climate risk section does not sit in isolation from strategy, financial planning, capital allocation or risk management.

Where a company uses a shadow carbon price or internal fee, our internal carbon pricing guide explains how to test whether that number is actually shaping capital allocation and transition-risk decisions.

Second, they are bounded. The company explains which entities, activities, geographies and time horizons are covered, and where uncertainty remains.

Third, they are decision-useful. The disclosure helps a reader understand whether management has identified the relevant risks and opportunities, whether it is monitoring them, and whether the company's strategy is resilient enough.

That is the difference between a sustainability narrative and investor-grade disclosure.

Why ISSB matters now

ISSB matters in 2026 because it is becoming the reference point for many national and market-level sustainability disclosure regimes. The standards are already issued, implementation support exists, and regulators are deciding how to use the baseline.

For the adoption picture rather than the standards themselves, read our ISSB adoption progress check. It tracks how IFRS Sustainability Disclosure Standards are moving into jurisdiction-level reporting routes, and why adoption visibility is not the same thing as comparable company data.

The United Kingdom is one example. UK Sustainability Reporting Standards are based on ISSB standards, while the Financial Conduct Authority (FCA) has been consulting on moving listed company climate disclosure rules away from existing TCFD-aligned requirements and toward UK SRS-based disclosure. That does not mean every UK company is automatically in scope, but it does show the direction of travel.

There is also a practical market reason. Investors want to compare companies across jurisdictions. If one company reports climate risk through polished narrative and another reports it through structured, financially material disclosure, the second company may be easier to assess.

That does not make ISSB perfect. It will not answer every impact question. It will not replace local law. It will not remove judgement from materiality assessments. But it does raise the bar for companies that want sustainability information to be treated as credible financial information.

ISSB readiness checklist

Before treating an ISSB workstream as ready, a company should be able to answer the following questions in ordinary business language, not only in reporting jargon.

For teams starting from evidence collection, the ESG data room checklist is often a practical first step. For climate metrics, read Scope 1, 2 and 3 emissions explained. For the resilience question, use the climate scenario analysis guide to check whether scenario assumptions are connected to business decisions.

Bottom line

ISSB is best understood as the global baseline for investor-focused sustainability disclosure. IFRS S1 sets the general architecture. IFRS S2 applies it to climate. Together, they move sustainability information closer to the discipline of financial reporting.

The strongest lesson for companies is not that another acronym has arrived. It is that sustainability information is becoming harder to keep separate from governance, risk, strategy, finance and audit-quality evidence.

FAQ

What does ISSB stand for?

ISSB stands for International Sustainability Standards Board. It is the IFRS Foundation board that develops IFRS Sustainability Disclosure Standards.

What is the difference between IFRS S1 and IFRS S2?

IFRS S1 sets general requirements for sustainability-related financial disclosures. IFRS S2 focuses specifically on climate-related risks and opportunities.

Is IFRS S2 the same as TCFD?

No. IFRS S2 builds on the Task Force on Climate-related Financial Disclosures structure, but it is a formal climate disclosure standard issued by the International Sustainability Standards Board.

Does ISSB use double materiality?

ISSB focuses on sustainability-related risks and opportunities that could affect an entity's prospects and are useful to capital providers. Corporate Sustainability Reporting Directive (CSRD) and European Sustainability Reporting Standards (ESRS) use double materiality, which also considers the company's impacts on people and the environment.

Are ISSB standards mandatory in the UK?

UK Sustainability Reporting Standards are based on ISSB standards, and UK regulators are deciding how to apply them in specific regimes. Companies should check current UK rules, FCA requirements and sector-specific obligations before assuming they are in scope.

Does IFRS S2 require Scope 3 emissions disclosure?

IFRS S2 includes greenhouse gas emissions disclosures, including Scope 1, Scope 2 and Scope 3 where required by the standard and subject to applicable reliefs. Companies should document methods, boundaries, assumptions and data quality.

Useful source links

• IFRS Foundation: International Sustainability Standards Board
• IFRS S1 General Requirements for Disclosure of Sustainability-related Financial Information
• IFRS S2 Climate-related Disclosures
• IFRS Foundation: use of IFRS Sustainability Disclosure Standards by jurisdiction
• IFRS Foundation: Inaugural Jurisdictional Guide for adoption or other use of ISSB Standards
• IFRS Foundation: supporting materials for IFRS Sustainability Disclosure Standards
• IFRS Foundation: TCFD and ISSB
• GOV.UK: government response on UK Sustainability Reporting Standards
• Financial Conduct Authority: CP26/5 sustainability disclosures consultation