What Is ISSB? IFRS S1 and S2 Explained for Sustainability Teams (2026)

TL;DR — ISSB in 60 seconds. The International Sustainability Standards Board (ISSB) is the body inside the IFRS Foundation that writes a global baseline for sustainability disclosure aimed at investors. It has issued two standards: IFRS S1 (general sustainability-related financial information) and IFRS S2 (climate-related disclosures, including Scope 1, 2 and 3 emissions and scenario analysis). As of 1 January 2026, 21 jurisdictions have adopted the standards on a voluntary or mandatory basis and nearly 40 are taking steps toward adoption, per S&P Global Sustainable1’s tracker. ISSB is not the EU’s ESRS, and it is not GRI — it answers a different question, for a different audience.

If you read only one paragraph, that’s it. The rest of this article explains where ISSB came from, what each standard covers, where it is mandatory in 2026, how it relates to ESRS and GRI, and what a sustainability team should do first.

Where ISSB came from: the consolidation story

For years, “sustainability reporting” meant choosing between alphabet soup — TCFD, SASB, CDP, GRI, IIRC, CDSB. Each framework solved a piece of the problem. None of them was the answer for an investor trying to compare a German automaker to a Japanese trading house to a Brazilian bank.

The IFRS Foundation — the body that already oversees IFRS Accounting Standards used in 140+ jurisdictions — was asked at COP26 to fix this. It announced the ISSB in November 2021, absorbed the Climate Disclosure Standards Board (CDSB) and the Value Reporting Foundation (which brought SASB and the Integrated Reporting Framework with it), and on 26 June 2023 issued its first two standards, IFRS S1 and IFRS S2.

The Task Force on Climate-related Financial Disclosures (TCFD) — the framework most multinationals had been using since 2017 — finished its work the next month. The Financial Stability Board transferred TCFD monitoring responsibilities to the IFRS Foundation from 2024, and TCFD itself disbanded in October 2023.

The point is not historical trivia. The point is that a company already disclosing under TCFD is most of the way to IFRS S2 — the four pillars (governance, strategy, risk management, metrics and targets) are preserved, with sharper requirements on industry-specific metrics and Scope 3 emissions.

IFRS S1: general requirements

IFRS S1 is the umbrella. It tells a company how to disclose sustainability-related risks and opportunities that could reasonably be expected to affect its cash flows, access to finance, or cost of capital over the short, medium, or long term.

Three things matter most:

Materiality is financial. S1 asks what is decision-useful to investors and other capital providers — not to society, regulators, or stakeholders broadly. This is a deliberate scope choice that distinguishes ISSB from the EU’s ESRS (see below) and from GRI.
Disclosures sit with the financial statements. Sustainability information must be reported as part of the company’s general-purpose financial reporting, at the same time as the financial statements, and connected to the same entity boundary.
All sustainability topics are in scope, not just climate. S1 sets the architecture. S2 is the first topic-specific standard. Biodiversity, human capital, and other topics will follow.

A company applying S1 must explain its governance over sustainability risks, the strategy for managing them, the risk-management process, and the metrics and targets used to measure performance — across every material sustainability topic, not only climate.

IFRS S2 is where most of the operational work lives. It requires a company to disclose:

Governance of climate risks and opportunities, including board oversight and management’s role.
Strategy, including how climate-related risks and opportunities affect the business model, value chain, and financial position — and how the strategy holds up under different climate scenarios.
Risk management, including how climate risks are identified, assessed, prioritised and integrated with the company’s overall risk-management process.
Metrics and targets, including absolute Scope 1, Scope 2 and Scope 3 greenhouse-gas emissions disclosed in line with the GHG Protocol, internal carbon prices used in decision-making, the proportion of executive remuneration linked to climate considerations, and progress against any climate-related targets the company has set.

Two requirements catch most first-time reporters off guard. The first is Scope 3 — emissions from the value chain — which IFRS S2 makes mandatory (with relief for the first year of application). The second is scenario analysis — a forward-looking assessment of strategic resilience under at least one climate scenario, which the ISSB has explicitly affirmed as a core requirement, even after issuing targeted amendments in December 2025 to ease implementation.

Who has to comply in 2026

This is the question every CSO gets asked first. As of 1 January 2026, requirements are already in effect in 19 jurisdictions, and 21 have formally adopted the standards on a voluntary or mandatory basis, according to the IFRS Foundation’s jurisdictional profiles.

A few 2026 milestones worth pinning to the wall:

Chile, Qatar and Mexico — mandatory rules referencing ISSB came into effect at the start of 2026.
Hong Kong — issuers on the Hong Kong Stock Exchange moved to a comply-or-explain regime in January 2025, with phased mandatory reporting based on IFRS S2 from 2026 onward.
Brazil — the securities regulator (CVM) issued resolutions requiring ISSB-aligned climate disclosures for listed companies on a phased basis starting FY 2026.
China — the Ministry of Finance issued a climate disclosure standard based on IFRS S2 on 25 December 2025.
Japan — the Sustainability Standards Board of Japan (SSBJ) released its inaugural standards in March 2025, fully incorporating IFRS S1 and S2 with jurisdiction-specific alternatives. The FSA is expected to require first reports for the fiscal year ending March 2027 from Prime-listed companies with market capitalisation at or above JPY 3 trillion.

For a current country-by-country tracker, see our ISSB Adoption Tracker. For the Japan-specific timeline and SSBJ alternatives, see SSBJ vs ISSB: What Japanese Companies Need to Know.

ISSB vs ESRS vs GRI: what’s the difference?

Three frameworks, three answers to three different questions.

Dimension	ISSB (IFRS S1/S2)	ESRS (EU CSRD)	GRI
Audience	Investors and capital providers	Investors and stakeholders	Stakeholders broadly
Materiality	Financial (single materiality)	Double materiality — financial and impact	Impact materiality
Scope	Climate now; other topics coming	Full ESG: 10 topical standards (E1–E5, S1–S4, G1)	Full ESG: ~35 topic standards
Geographic anchor	Global baseline	EU regulation (extraterritorial)	Global voluntary
Where it sits	Part of financial reporting	Management report	Standalone sustainability report

The two regulatory frameworks — ISSB and ESRS — are not rival systems trying to replace each other. The IFRS Foundation and EFRAG published joint interoperability guidance on 2 May 2024 showing the high level of alignment on climate disclosure. The core distinction remains: ESRS requires a double materiality assessment (financial and impact), while ISSB requires only the financial side. A company doing ESRS properly will produce ISSB-aligned disclosures as a subset.

For a deeper side-by-side, see our GRI vs ISSB vs ESRS comparison. For how the EU’s revised CSRD scope intersects with ISSB timelines, see the EU Omnibus 2026 explainer.

Common pitfalls

Three failure modes show up repeatedly in first-year ISSB-aligned reports:

Treating IFRS S2 as a TCFD refresh. It is and it isn’t. The four pillars are familiar, but mandatory Scope 3, industry-based metrics, and connected-information requirements raise the bar significantly. Audit firms are also more demanding than the voluntary TCFD era.
Underestimating value-chain data. Scope 3 is the line item that breaks timelines. Companies that have not begun supplier engagement, primary-data collection, or estimation methodologies will not produce credible numbers in their first reporting cycle. Start a year earlier than you think you need to.
Disconnecting sustainability from financial reporting. S1 is explicit: the same entity boundary, the same reporting period, the same governance and controls as the financial statements. Sustainability data that lives in a separate spreadsheet, on a separate timeline, controlled by a separate team will fail assurance.

Where to start: three concrete first steps

If your company is in scope for 2026 or 2027 — or simply preparing voluntarily — the practical sequence looks like this.

Run a gap analysis against IFRS S2. Map what TCFD-aligned disclosures already exist, where Scope 3 data lives (or doesn’t), and what scenario analysis the company has done. Our CSRD gap analysis guide applies almost directly — the discipline transfers.
Fix the data foundation before the narrative. Almost every ISSB-related failure traces back to non-auditable data. Inventory the systems, define controls, and decide which data points need primary collection vs. estimation. AI helps — see how AI processes raw sustainability data into ESRS-ready disclosures — but only on top of clean inputs.
Connect to your financial reporting calendar. S1 requires sustainability information to be published at the same time as financial statements. That has implications for close cycles, audit-committee oversight, and assurance procurement. Treat it as a financial-reporting workstream, not a CSR project.

ISSB is not the end of the alphabet soup. But it is the first global baseline that finance, sustainability, and investor-relations teams can all point at and mean the same thing. For most companies, the question is no longer “will we report under ISSB” — it is “are our systems ready when our jurisdiction switches on.”

If you want a closer look at how AI-native sustainability reporting handles ISSB, ESRS and SSBJ in a single pipeline, explore Socious Report or book a 20-minute walk-through. The earlier you have an audit trail you trust, the easier the rest of this gets.