Independent Assurance Statement: What It Is and What It Contains

As sustainability reporting becomes regulated and investor-critical, the independent assurance statement is emerging as one of the most important documents in corporate ESG disclosure. Yet many sustainability professionals, investors, and procurement managers do not fully understand what an assurance statement is, what it should contain, or how to evaluate its quality.

This guide provides a comprehensive explanation of independent assurance statements — their purpose, structure, conclusion types, and the practical skills needed to read them critically.

What Is an Independent Assurance Statement?

An independent assurance statement is the formal written conclusion issued by a qualified, independent assurance provider after completing an assurance engagement on an organisation's sustainability report or specific sustainability disclosures.

It serves the same function for sustainability data that an audit opinion serves for financial statements: it tells the reader whether, in the professional judgement of an independent expert, the reported information is fairly stated and free from material misstatement.

Key Characteristics

• Independence: The provider has no financial, advisory, or operational relationship with the reporting organisation that could compromise objectivity
• Standards-based: The engagement is conducted in accordance with recognised assurance standards (ISAE 3000, ISAE 3410, AA1000AS, or ISSA 5000)
• Evidence-based: The conclusion is supported by evidence gathered through structured procedures — not simply a review of the published report
• Scope-defined: The statement clearly identifies what was assured and what was not
• Formally concluded: The statement contains a formal conclusion in standardised language

What It Is Not

An assurance statement is not:

• A validation that the company is "sustainable" or "doing enough"
• A guarantee that the data is 100% accurate
• A certification or seal of approval
• A review of strategy, targets, or ambition
• A legal opinion on regulatory compliance

It is a professional conclusion on whether the reported information is fairly stated in accordance with the applicable criteria, to the level of assurance specified.

Who Issues Assurance Statements?

Assurance statements are issued by qualified assurance providers. The market currently includes several types of providers:

Types of Assurance Providers

Under the CSRD, assurance providers must be either statutory auditors with sustainability assurance qualifications or Independent Assurance Services Providers (IASPs) accredited by national accreditation bodies. This is a significant change that will shape the assurance provider landscape. For guidance on selecting the right provider, see our article on how to choose a sustainability assurance provider.

Standard Structure of an Assurance Statement

A well-structured independent assurance statement follows a standardised format. While there is some variation between providers and standards, the following elements should be present in every statement:

1. Addressee

The statement begins by identifying to whom it is addressed — typically the board of directors, the audit committee, or the management of the reporting organisation. This establishes who the intended users of the statement are.

2. Scope of the Engagement

This is arguably the most critical section. The scope defines:

• The specific subject matter assured (e.g., "selected sustainability performance indicators as presented in the 2024 Sustainability Report")
• The reporting period covered
• The reporting boundaries (which entities, operations, or geographies are included)
• Any specific indicators, disclosures, or sections covered
• Any explicit exclusions from scope

Readers must pay careful attention to scope. A statement that assures "selected indicators" is very different from one that assures the entire sustainability report.

3. Applicable Criteria

The criteria section identifies the reporting framework or standards against which the information was assessed. Common criteria include:

• GRI Standards (2021)
• European Sustainability Reporting Standards (ESRS)
• GHG Protocol Corporate Standard
• IFRS S1/S2 (ISSB Standards)
• Company-specific reporting criteria

4. Level of Assurance

The statement must clearly state whether the engagement provides limited assurance or reasonable assurance. This determines the depth of procedures and the form of the conclusion.

5. Management's Responsibilities

This section clarifies that management is responsible for the preparation of the sustainability information, the selection of reporting criteria, and the design of internal controls. The assurance provider does not take responsibility for the data — they evaluate it.

6. Assurance Provider's Responsibilities

This describes the provider's responsibility to plan and perform the engagement in accordance with the applicable assurance standard and to express a conclusion based on the evidence obtained.

7. Summary of Procedures Performed

The statement should describe, at least in summary, what the assurance provider did. Typical procedures include:

• Inquiries of management and sustainability personnel
• Analytical procedures on sustainability data
• Review of documentation and evidence
• Testing of data aggregation and calculations
• Site visits (if applicable)
• Review of internal controls over sustainability data
• Comparison of reported data to source records

8. Independence and Competence Declaration

The provider must confirm their independence from the reporting organisation and declare their qualifications, accreditation, and competence to perform sustainability assurance engagements.

9. Conclusion

The formal conclusion is the core output of the statement. Its form depends on the level of assurance and whether any issues were identified. This is explained in detail in the sections below.

10. Date, Signature, and Provider Identification

The statement is dated (typically the date procedures were completed), signed by the engagement leader, and identifies the assurance provider by name, address, and relevant accreditation.

Levels of Assurance: Limited vs Reasonable

The two levels of assurance — limited and reasonable — differ fundamentally in the depth of work performed and the confidence the conclusion provides.

Conclusion Types: Clean, Qualified, and Adverse

Clean (Unmodified) Conclusion

A clean conclusion means the assurance provider found no material misstatements. The sustainability information is fairly stated in accordance with the applicable criteria. This is the outcome most reporting organisations aim for and the one most commonly issued.

Qualified (Except-For) Conclusion

A qualified conclusion means the assurance provider identified a specific material misstatement or was unable to obtain sufficient evidence on a specific matter, but the issue is not pervasive enough to affect the entire report. The conclusion states that "except for" the identified matter, the information is fairly stated.

Qualifications are relatively rare in published assurance statements, partly because they can be avoided through correction of identified issues before the statement is finalised. When they appear, they signal a specific, identified problem that readers should investigate.

Adverse Conclusion

An adverse conclusion means the assurance provider found material misstatements that are pervasive — the sustainability information as a whole is materially misstated. Adverse conclusions are extremely rare in published reports, because most organisations would correct the issues rather than publish an adverse statement.

Disclaimer of Conclusion

A disclaimer is issued when the assurance provider was unable to obtain sufficient evidence to form any conclusion. This typically results from severe scope limitations — the provider was denied access to records, personnel, or sites needed to perform their procedures. A disclaimer is a serious matter and suggests fundamental problems with the engagement or the organisation's cooperation.

Practical Examples of Conclusion Wording

Limited Assurance — Clean Conclusion

Reasonable Assurance — Clean Conclusion

Limited Assurance — Qualified Conclusion

How Investors and Buyers Interpret Assurance Statements

For investors, lenders, customers, and procurement professionals, the ability to critically evaluate an assurance statement is increasingly important. Here is a structured approach:

Step 1: Check the Scope

Before reading anything else, determine exactly what was assured. Was it the full sustainability report, or only selected indicators? Does it cover all material topics, or just environmental data? Are all entities and operations included, or only certain geographies?

Step 2: Verify the Level of Assurance

Limited assurance is the most common level. If you are comparing two companies, one with limited assurance and one with reasonable assurance, the latter's data carries significantly more weight.

Step 3: Examine the Criteria

Assurance against recognised standards (GRI, ESRS, GHG Protocol) is more meaningful than assurance against "company-specific criteria," which may be less rigorous.

Step 4: Review Procedures

Look at what the provider actually did. Did they visit sites? Did they test data back to source records? Engagements limited to "desk-based review and management inquiry" provide less confidence than those involving substantive testing.

Step 5: Evaluate the Provider

Is the provider accredited? Do they have demonstrated sustainability assurance experience? Are they genuinely independent from the reporting organisation?

Step 6: Read the Conclusion Carefully

Is it clean, qualified, or adverse? Are there emphasis of matter paragraphs that highlight uncertainties? Does the conclusion language match standard ISAE 3000 or AA1000AS wording?

What a Good vs Weak Assurance Statement Looks Like

Red Flags in Assurance Statements

When reviewing assurance statements — whether as an investor, buyer, board member, or sustainability professional — watch for these warning signs:

Scope Red Flags

• Cherry-picked indicators: Only easy-to-verify metrics are in scope, while material topics like Scope 3 emissions, human rights, or supply chain labour practices are excluded
• Geographic exclusions: High-risk operations or geographies are excluded from the assurance scope
• Forward-looking claims in scope: Targets and commitments presented as assured, when in reality only historical data can be assured

Independence Red Flags

• Self-review threat: The assurance provider also prepared or consulted on the sustainability report — a fundamental conflict of interest
• No independence declaration: The statement does not explicitly confirm the provider's independence
• Long tenure without rotation: The same individual or firm has provided assurance for many years without rotation

Quality Red Flags

• Boilerplate language: The statement reads as a generic template with no engagement-specific content
• No procedures described: The reader cannot determine what the provider actually did
• Missing accreditation: The provider's qualifications and accreditation are not disclosed
• Undated or unsigned: The statement lacks a date, signature, or provider identification
• Marketing tone: The conclusion is mixed with promotional language about the company's sustainability leadership

GRI Content Index Alignment

For organisations reporting under the GRI Standards, the assurance statement should align with GRI 2: General Disclosures 2021, Disclosure 2-5 (External assurance).

What GRI Requires

Disclosure 2-5 requires organisations to:

• Describe the organisation's policy and practice for seeking external assurance
• Provide a link to or reproduction of the external assurance statement(s)
• Describe what topics, disclosures, or information are covered by external assurance
• Describe the relationship between the organisation and the assurance provider

Best Practice Integration

In best practice, the assurance statement and the GRI Content Index should cross-reference each other. The Content Index should indicate which disclosures have been externally assured and reference the statement. The statement should confirm that it covers the specific GRI disclosures identified in the Content Index.

When assurance covers the materiality process (GRI 3: Material Topics), the provider confirms that the organisation has followed a robust process for identifying material topics — adding credibility to the entire report's focus and completeness.

Reading Between the Lines

Experienced readers of assurance statements look beyond the formal conclusion to understand the nuances:

Emphasis of Matter Paragraphs

These paragraphs draw attention to matters that are appropriately presented in the report but that the assurance provider considers important for readers to understand. Common subjects include:

• Significant estimation uncertainty (e.g., Scope 3 emissions calculations using industry-average emission factors)
• Changes in reporting methodology from previous periods
• Restatement of prior year data
• Inherent limitations of the subject matter

An emphasis of matter paragraph does not modify the conclusion, but it signals that the reader should exercise judgement when interpreting the assured information.

Other Matter Paragraphs

These highlight matters relevant to the reader's understanding of the engagement itself (as opposed to the subject matter). Common examples include:

• Restrictions on use of the statement
• The fact that prior year data was assured by a different provider
• Inherent limitations of limited assurance procedures

What the Scope Excludes Tells You

Sometimes what is not in the scope of assurance is as informative as what is. If a company's sustainability report covers environmental, social, and governance topics but only the environmental data is assured, readers should question why social and governance disclosures were excluded. If Scope 3 emissions — often the largest emissions category — are excluded from an otherwise comprehensive greenhouse gas assurance, the carbon footprint figures should be interpreted with caution.