IAASB publishes ISSA 5000 illustrative reports to support sustainability assurance

The International Auditing and Assurance Standards Board published a suite of eight illustrative assurance reports in late 2025 to support implementation of ISSA 5000, its global sustainability assurance standard finalised in November 2024. Indian companies should strengthen internal controls over ESG data ahead of the standard's effective date for periods beginning on or after December 15 2026 to avoid modified assurance conclusions.

The IAASB published the final International Standard on Sustainability Assurance (ISSA) 5000, General Requirements for Sustainability Assurance Engagements, in November 2024, establishing a global baseline for assurance over reported ESG information. The standard is profession-agnostic and framework-neutral, applicable under any reporting criteria including IFRS S-series and the European Sustainability Reporting Standards. It is generally effective for engagements reported for periods beginning on or after December 15 2026. In late 2025, the IAASB published eight illustrative assurance reports developed with jurisdictional standard setters to support practical implementation.

The guidance affects companies reporting ESG information, professional accountants, and non-accountant assurance specialists. The eight illustrative reports cover common engagement scenarios: five with unmodified assurance conclusions, including engagements on disclosures aligned with IFRS S1 and S2 under both limited and reasonable assurance, reports on selected sustainability disclosures, reports using multiple reporting frameworks, and a combined limited and reasonable assurance report. Three further examples cover modified conclusions, demonstrating how practitioners communicate qualified conclusions, disclaimers, or adverse conclusions when material misstatements or scope limitations are identified.

Companies should immediately strengthen internal controls over ESG data collection and reporting to avoid modified assurance conclusions ahead of the December 15 2026 effective date for periods beginning on or after that date, while monitoring whether local jurisdictions mandate or permit earlier application. Preparers should review the illustrative reports to understand assurance expectations under their chosen frameworks. For investors, comparable, consistently rigorous assurance reports across jurisdictions and frameworks will enhance confidence in disclosed information, combat greenwashing, and facilitate informed capital-allocation decisions.

Key figure — Effective date: assurance engagements for periods beginning on or after December 15 2026