ESRS vs ISSB: Understanding the Two Major Sustainability Standards

If you're responsible for sustainability reporting, you've likely encountered two acronyms that dominate the conversation: ESRS and ISSB. Both represent landmark efforts to standardize sustainability disclosures, yet they take fundamentally different approaches. Understanding these differences—especially following the EU's December 2025 Omnibus simplification—is essential for any organization seeking an effective ESRS compliance tool or broader sustainability reporting strategy.

The EU Omnibus: A Game-Changer for ESRS

Before diving into the comparison, it's crucial to understand how the regulatory landscape has shifted. The EU Omnibus Simplification Package (agreed December 2025) fundamentally transformed CSRD and ESRS implementation:

What Changed

Reduced Scope: The number of companies in scope dropped dramatically from approximately 50,000 to large EU companies meeting both thresholds: over 1,000 employees AND over EUR 450 million turnover. Listed SMEs have been removed from scope entirely.

Simplified Materiality Assessment: The double materiality process has been streamlined. While the concept remains, the assessment methodology is now more proportionate and less burdensome, with clearer thresholds for determining what qualifies as material.

Phased Timeline (Post-Omnibus):

• 2025 reports (due 2026): Large public-interest entities (>1,000 employees & >EUR 450M turnover)
• 2026 reports (due 2027): Other large companies meeting both thresholds

Reduced Datapoint Requirements: Many disclosure requirements have been made voluntary or sector-specific rather than mandatory for all companies. The core mandatory disclosures are now more focused on genuinely material information.

Value Chain Cap: Companies with fewer than 1,000 employees are now protected from excessive sustainability information requests. Large reporters can only request information from smaller suppliers in accordance with the Voluntary SME Standard (VSME), preventing disproportionate burden on supply chains.

Assurance Simplified: The original requirement to transition from limited to reasonable assurance by 2028 has been permanently removed. ESRS reports will remain under limited assurance only, reducing compliance costs.

Enhanced Flexibility: Greater proportionality for medium-sized companies and more flexibility in how companies demonstrate compliance with disclosure requirements.

All information in this article reflects the post-Omnibus simplified ESRS framework (November 2025).

The Origins: Two Paths to the Same Goal

ESRS (European Sustainability Reporting Standards) emerged from the EU's Corporate Sustainability Reporting Directive (CSRD), adopted in late 2022 and subsequently refined through the 2025 Omnibus package. Developed by the European Financial Reporting Advisory Group (EFRAG), the 12 ESRS standards reflect the EU's broader sustainability agenda—extending beyond climate to encompass environmental, social, and governance topics comprehensively.

ISSB (International Sustainability Standards Board) was established by the IFRS Foundation in 2021, building on the momentum of TCFD and consolidating earlier initiatives like SASB and the CDSB. The ISSB released IFRS S1 (General Requirements) and IFRS S2 (Climate-related Disclosures) in June 2023, with a clear focus on investor-relevant information.

Both frameworks aim to improve comparability and decision-usefulness of sustainability information. However, their philosophical foundations differ significantly.

The Core Difference: Double vs Single Materiality

The most fundamental distinction between ESRS and ISSB lies in their materiality approach.

ESRS: Double Materiality (Simplified)

ESRS requires companies to report on sustainability matters that are material from two perspectives:

1. Impact materiality: How your company's activities affect people and the environment (inside-out view)
2. Financial materiality: How sustainability matters create risks and opportunities that affect your enterprise value (outside-in view)

A topic is material under ESRS if it meets either threshold. The Omnibus simplification has clarified the assessment process and raised thresholds, meaning fewer topics may qualify as material for smaller in-scope companies.

ISSB: Single (Financial) Materiality

ISSB takes a narrower approach, focusing exclusively on information that could reasonably influence investor decisions. Under IFRS S1 and S2, a sustainability matter is material only if omitting or misstating it could influence investment decisions.

This doesn't mean ISSB ignores broader impacts—but it frames them through the lens of financial risk and opportunity. Climate change matters because it affects asset values and business models, not because of its intrinsic environmental significance.

Comparison Table: ESRS vs ISSB at a Glance

Where They Overlap

Despite their differences, ESRS and ISSB share substantial common ground:

Climate Disclosure Alignment

ESRS E1 (Climate Change) and IFRS S2 (Climate-related Disclosures) both build on TCFD's four-pillar structure: Governance, Strategy, Risk Management, and Metrics & Targets. Companies reporting under both frameworks will find significant overlap in climate disclosure requirements—though ESRS demands additional granularity on Scope 3 emissions and transition plans.

Governance and Strategy

Both frameworks require disclosure of:

• Board and management oversight of sustainability matters
• Integration of sustainability into strategy and business model
• Risk management processes for identifying and managing sustainability risks
• Metrics and targets used to assess performance

Interoperability Commitment

EFRAG and ISSB have formally committed to interoperability. The EU has confirmed that ESRS disclosures can satisfy ISSB requirements for EU companies, and mapping guidance exists to help companies demonstrate dual compliance efficiently.

Industry-Specific Guidance: The SASB Connection

A key difference: ISSB inherited the SASB Standards when the Value Reporting Foundation merged into the IFRS Foundation in 2022. Companies applying IFRS S1 are required to consider SASB Standards for identifying sustainability risks and opportunities beyond climate—covering topics like water management, workforce health, and data security across 77 industries.

The ISSB is actively enhancing these standards, with comprehensive reviews of priority industries underway. S3 (biodiversity) has moved to active standard-setting as of January 2026, while S4 (human capital) remains in the research phase. ESRS sector-specific standards are still being developed, making SASB the current go-to for industry-specific guidance globally.

Practical Implications for Reporters

If You're a Large EU Company (Post-Omnibus)

Check whether you're still in scope under the revised thresholds. If you are, ESRS compliance is mandatory, but the simplified requirements mean fewer mandatory datapoints and a more proportionate materiality assessment. The good news: if you meet ESRS requirements, you'll likely satisfy most ISSB requirements as well.

If You're Global with EU Operations

You may face dual compliance. Some jurisdictions (UK, Singapore, Hong Kong, Australia, Brazil) are adopting ISSB-based requirements, while your EU subsidiary or EU revenue exposure may still trigger CSRD/ESRS obligations depending on size thresholds.

If You're Outside the EU

ISSB is increasingly the global baseline. Countries representing over 50% of global GDP have announced adoption pathways. Starting with IFRS S1 and S2 prepares you for the most likely regulatory trajectory.

Navigating Both: A Compliance Strategy

For organizations facing both ESRS and ISSB requirements:

1. Understand your scope first. Post-Omnibus, many companies previously expecting ESRS obligations may no longer be in scope. Verify your status before investing in compliance infrastructure.

2. Conduct a streamlined materiality assessment. Use the simplified ESRS double materiality process. This covers ISSB's single materiality requirement as a subset.

3. Build a unified data architecture. Many datapoints overlap—Scope 1, 2, and 3 emissions, governance structures, target-setting processes. Collect once, report twice.

4. Start with climate. Both frameworks prioritize climate. Robust TCFD-aligned climate disclosure serves as the foundation for both ESRS E1 and IFRS S2 compliance.

5. Leverage SASB for beyond-climate topics. If you're an ISSB reporter, SASB Standards are your guide for industry-specific risks beyond climate. These standards are increasingly interoperable with ESRS.

6. Use gap analysis tools. Identify where your current reporting falls short against each framework's specific requirements. This is where AI-powered analysis can save significant time compared to manual mapping.

Key Takeaways

• The December 2025 Omnibus agreement significantly simplified ESRS, reducing in-scope companies, introducing value chain caps, and permanently keeping limited assurance (no transition to reasonable)
• ESRS uses double materiality (impact + financial); ISSB uses single materiality (financial only)
• Climate disclosures overlap significantly between ESRS E1 and IFRS S2, building on TCFD
• SASB is now integral to ISSB—companies must consider SASB Standards for beyond-climate topics under IFRS S1
• Dual compliance is feasible with strategic planning and unified data collection
• Check your post-Omnibus scope status before investing heavily in compliance

Ready to Analyze Your Report?

Understanding where your sustainability report stands against both ESRS and ISSB requirements is the first step toward compliance. Martin analyzes your report against 500+ disclosure requirements across both frameworks—covering ESRS and ISSB requirements, updated for the December 2025 ESRS simplification—identifying gaps and providing actionable recommendations.

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For more on EU-specific requirements, see our CSRD guide. For ISSB implementation details, explore our ISSB/IFRS S1 & S2 guide. For a deep dive on materiality approaches, see our single vs double materiality guide.