How to Write a Sustainability Report

Why This Matters

A sustainability report is your organization's primary vehicle for communicating environmental, social, and governance (ESG) performance to investors, regulators, customers, and employees. Done well, it builds trust and surfaces operational risks. Done poorly, it invites greenwashing accusations and regulatory scrutiny.

This guide walks you through writing a report that meets current disclosure expectations — whether you're reporting voluntarily or preparing for mandatory frameworks like the CSRD or ISSB standards.

Step 1: Define Your Reporting Scope and Boundaries

Before writing a single word, establish what your report covers:

• Organizational boundary: Use one of the GHG Protocol's consolidation approaches (equity share, financial control, or operational control). Be explicit about which entities are included.
• Reporting period: Align with your fiscal year. If this is your first report, pick a 12-month baseline.
• Topic boundary: Identify which ESG topics are material to your business. This feeds directly from your materiality assessment (see our separate how-to guide on that topic).

Document these decisions upfront. Reviewers and assurance providers will scrutinize inconsistencies between your stated scope and the data you present.

Step 2: Conduct a Materiality Assessment

If you haven't already, run a materiality assessment to identify which topics warrant disclosure. Under GRI, this means identifying topics where your organization has the most significant impacts on the economy, environment, and people. Under ISSB/IFRS S1, it means identifying sustainability-related risks and opportunities that could reasonably affect your enterprise value.

For CSRD reporters, you need a double materiality assessment covering both impact materiality and financial materiality. The European Sustainability Reporting Standards (ESRS) require specific disclosure requirements tied to each material topic.

The output of this step is a prioritized list of topics that determines the structure and depth of your report.

Step 3: Gather Data

This is where most first-time reporters struggle. Build a data collection plan that covers:

• Environmental data: GHG emissions (Scopes 1, 2, 3), energy consumption, water withdrawal, waste generation, land use
• Social data: Workforce demographics, health and safety metrics, training hours, living wage analysis, human rights due diligence findings
• Governance data: Board composition, executive compensation tied to sustainability targets, anti-corruption policies, lobbying expenditures

Use standardized collection templates. The GRI Content Index is a useful checklist. For emissions specifically, follow the GHG Protocol Corporate Standard and use emission factors from recognized sources (EPA, the UK government's DESNZ factors, IEA, ecoinvent).

Assign data owners for each metric. Set internal deadlines at least 8 weeks before your publication target.

Step 4: Choose Your Framework(s)

Pick one or more reporting frameworks based on your audience and regulatory obligations:

• GRI Standards (2021): Best for stakeholder-facing reports covering broad ESG topics. Widely recognized globally.
• ISSB (IFRS S1 and S2): Investor-focused. Effective for periods from January 2024; as of April 2026, 28 jurisdictions had adopted them in some form.
• ESRS (under CSRD): Mandatory for companies in CSRD scope (after the 2026 Omnibus I changes, more than 1,000 employees and more than €450 million in net turnover). Highly prescriptive with specific datapoints; revised, simplified ESRS apply from financial year 2027.
• CDP: A single scored questionnaire (since 2024) covering climate, water, forests and more. Often requested by institutional investors and supply chain partners.

You can report under multiple frameworks simultaneously. The GRI-ISSB interoperability guidance on GHG emissions and the joint GRI-ESRS Interoperability Index make this feasible without duplicating work.

Step 5: Structure Your Report

A credible sustainability report typically includes:

1. CEO/Chair message — Sets tone, references specific targets and outcomes (not vague aspirations)
2. Company profile — Business model, value chain, geographic footprint
3. Governance — ESG oversight structure, board competencies, risk management integration
4. Strategy — How sustainability issues affect business strategy, scenario analysis (especially for climate under TCFD/ISSB)
5. Material topics — For each material topic: management approach, policies, targets, performance data, and year-over-year trends
6. Data tables — Consolidated metrics with clear units, scope, methodology notes
7. GRI Content Index / ESRS index — Maps your disclosures to specific framework requirements
8. Assurance statement — If you've obtained third-party assurance (increasingly expected)

Step 6: Write Clear, Specific Content

The biggest mistake in sustainability reporting is vague language. Apply these principles:

• Lead with numbers. "We reduced Scope 1 emissions by 12% against a 2019 baseline" beats "We made progress on our climate goals."
• Acknowledge gaps. If you don't have Scope 3 data for a category, say so and explain your plan to close the gap. Readers respect honesty over omission.
• Avoid jargon without context. Define terms like "science-based target" or "double materiality" if your audience includes non-specialists.
• Show trends. Three or more years of data demonstrates trajectory, not just a snapshot.
• Be balanced. Disclose negative performance alongside positive. Cherry-picking erodes credibility.

Step 7: Internal Review and Quality Assurance

Before publication:

• Run a completeness check against your chosen framework's disclosure requirements
• Have finance review all quantitative claims
• Legal should review forward-looking statements and any regulatory compliance claims
• Conduct an internal "red team" review — would a skeptical journalist or analyst find contradictions?

Step 8: Seek External Assurance

Third-party assurance is becoming table stakes. Under CSRD, limited assurance is mandatory from year one; the 2026 Omnibus I directive dropped the planned transition to reasonable assurance. Several ISSB-adopting jurisdictions also require assurance, and Australia, for example, moves to reasonable assurance by the fourth year of reporting.

Engage an assurance provider early — ideally during data collection — so they can review your processes, not just your final numbers. Common standards for assurance include ISAE 3000 (Revised), AA1000 Assurance Standard, and the IAASB's ISSA 5000 (issued November 2024; effective for periods beginning on or after December 15, 2026).

Step 9: Publish and Distribute

Publish your report in an accessible format (PDF and web). Submit to relevant platforms:

• CDP portal (if applicable)
• GRI's Report Registration System (notifying GRI is a mandatory step when you report with the GRI Standards)
• Your company website's investor relations or sustainability section
• Regulatory filing channels: CSRD reports are filed through national systems and, from January 2028, also become available on the European Single Access Point (ESAP), which ESMA runs

Step 10: Plan for Next Year

Treat each report as an iteration. After publication:

• Document lessons learned and data gaps
• Set improvement targets for next cycle
• Begin stakeholder engagement for the next materiality refresh
• Track regulatory changes that may affect future disclosures

Frequently Asked Questions

How long should a sustainability report be?

There's no fixed length. GRI-aligned reports that cover many material topics tend to run long. ISSB disclosures can be shorter since they focus on financially material topics. Prioritize clarity over length — a 40-page report with solid data beats a 200-page document padded with stock photos and mission statements.

Can we combine our sustainability report with our annual financial report?

Yes, and many companies are moving toward integrated reporting. ISSB standards are designed to sit alongside financial statements. CSRD disclosures are part of the management report within the annual report. Just ensure ESG content receives the same rigor as financial content.

Do we need third-party assurance for our first report?

If you're subject to CSRD, yes — limited assurance is mandatory. For voluntary reporters, assurance isn't strictly required but significantly boosts credibility. At minimum, have an internal audit team review your data and methodology.

What's the difference between GRI and ISSB reporting?

GRI focuses on your organization's impacts on the world (impact materiality) and serves a broad stakeholder audience. ISSB focuses on how sustainability issues affect your enterprise value (financial materiality) and primarily serves investors. Many organizations report under both — they address different questions.

How long does it take to produce a sustainability report?

First reports take the longest, because data owners, processes and pipelines are being built for the first time; later reports go faster as those mature. The biggest time sinks are data collection and internal review.