Sustainability Assurance Resources

What Is Sustainability Assurance?

Sustainability assurance is the independent, third-party examination of an organisation's sustainability report, ESG disclosures, or non-financial information. A qualified assurance provider evaluates whether reported information is materially correct, complete, and prepared according to applicable criteria — then issues a formal assurance statement expressing a limited or reasonable level of confidence.

With the EU Corporate Sustainability Reporting Directive (CSRD) now requiring mandatory limited assurance on ESRS-aligned reports — and reasonable assurance expected by 2028 — independent sustainability assurance has moved from a voluntary best practice to a regulatory imperative for thousands of companies worldwide.

• ISAE 3000 (Revised) — the IAASB's general standard for assurance engagements on non-financial information, widely adopted globally
• AA1000AS v3 — AccountAbility's stakeholder-centred assurance standard covering inclusivity, materiality, responsiveness, and impact
• ISSA 5000 — the IAASB's new dedicated sustainability assurance standard (effective December 2026), purpose-built for sustainability disclosures
• Limited vs Reasonable Assurance — understanding the difference in evidence, testing, and the form of the assurance conclusion
• CSRD Pre-Assurance — gap assessments and readiness programmes to prepare before formal assurance engagements begin
• ISO/IEC 17029 & ISO 14065 — conformity assessment standards underpinning credible third-party validation and verification bodies