ISSA 5000, ISAE 3410 or ISO 14064-3: which standard applies to my sustainability assurance?

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It depends on who gives the opinion and on what. Accountancy firms use IAASB standards: ISAE 3410 for a GHG statement, and ISSA 5000 for sustainability information as a whole. Verification bodies use ISO 14064-3 for GHG statements. You usually do not pick the standard; your regulator, buyer or assurance provider does. Issued by the International Auditing and Assurance Standards Board (IAASB) for assurance on a greenhouse gas statement. It covers limited and reasonable assurance and sets out procedures specific to emissions, such as testing activity data and emission factors. It is written for practitioners who follow the IAASB quality management and ethics framework. ISSA 5000, General Requirements for Sustainability Assurance Engagements, was issued by the IAASB in November 2024 and is effective for assurance on sustainability information for periods beginning on or after 15 December 2026. It covers any sustainability topic and any reporting framework, including ESRS, IFRS S2 and GRI, and it is written so that practitioners outside accountancy firms can also use it if they meet equivalent quality and ethics requirements. For a report that mixes emissions with social and governance metrics, ISSA 5000 is the natural fit. Check IAASB guidance on how ISAE 3410 is used alongside it once ISSA 5000 takes effect. ISO 14064-3:2019 sets out how to verify or validate GHG statements, for an organisation's inventory, a project or a product footprint. It is used by verification bodies, often accredited against ISO 14065, and by many carbon programmes and buyer schemes. It is a GHG-only standard. SEBI's BRSR Core framework requires reasonable assurance or assessment of the core KPIs for the largest listed companies, phased in by market capitalisation. Check the SEBI circulars for any requirement on the standard the provider uses. The Institute of Chartered Accountants of India issues its own sustainability assurance standard, SSAE 3000, which chartered accountants use. Watch for ICAI's response to ISSA 5000. Buyer programmes and carbon credit schemes often name ISO 14064-3 or their own verification rules. If a regulation or contract names a standard, use that one. Emissions only, assured by an accountancy firm: ISAE 3410, or ISSA 5000 for periods once it is effective. Emissions only, verified by a verification body or for a carbon programme: ISO 14064-3. Wider sustainability report: ISSA 5000, or SSAE 3000 for ICAI members in India.