The Wait Will Soon Be Over: Sustainability Assurance Is On Its Way

In today’s rapidly evolving sustainability reporting landscape, the demand for reliable, credible, and comparable sustainability information has never been greater. For some time, demand has been growing for more independently assured sustainability information that meets a globally recognised assurance standard, and with new sustainability standards and regulatory changes, assurance will be expected.

Well, the wait is almost over. The International Auditing and Assurance Standards Board (IAASB) has developed the International Standard on Sustainability Assurance (ISSA) 5000—a comprehensive framework designed to enhance the quality, consistency and reliability of sustainability assurance engagements.

What is ISSA 5000?
ISSA 5000 is a global assurance baseline standard designed to provide a robust and consistent approach to sustainability assurance. It sets out general requirements for performing high-quality limited or reasonable assurance engagements on sustainability reporting. The standard ensures that the assurance engagements that professional accountants and practitioners undertake in this space, is underpinned by rigorous quality management systems, aligned with the International Standard on Quality Management (ISQM) 1.

The development of ISSA 5000 was closely coordinated with the International Ethics Standards Board for Accountants (IESBA), resulting in a cohesive framework that places ethics and independence at its core to ensure high-quality sustainability assurance engagements.

Why Was ISSA 5000 Developed?
The rise in sustainability reporting and disclosure has been accompanied by growing concerns about greenwashing, misrepresentation, and inconsistencies in disclosures. As a result, independent assurance of this reporting has become critical, and therefore the ISSA 5000 standard looks to:

• Provide a global baseline for sustainability assurance engagements.
• Address market and regulatory demands for profession-agnostic sustainability standards.
• Enhance public confidence in sustainability information.
• Reduce the risks associated with misleading or unreliable sustainability disclosures.
• Support transparency and comparability across different reporting frameworks

Who Does ISSA 5000 Apply To?
ISSA 5000 applies to all sustainability assurance practitioners, including:

• Professional accountants conducting sustainability assurance engagements.
• Other sustainability assurance professionals providing independent assurance services.
• Practitioners using the work of external experts in sustainability assurance engagements.

The Key Features Of ISSA 5000
Quality Management: ISSA 5000 is built on ISQM 1, requiring firms to establish and maintain systems of quality management to ensure high-quality assurance engagements.

Ethics And Independence: The IESSA establishes ethical requirements, ensuring that sustainability assurance professionals act with integrity and objectivity.

Comprehensive Engagement Process: ISSA 5000 provides guidance from engagement acceptance to reporting, ensuring a structured and consistent approach.

Framework-Neutral Approach: The standard can be applied across various sustainability reporting frameworks, such as the ISSB IFRS Sustainability Disclosure Standards, European Sustainability Reporting Standards (ESRS), and the Global Reporting Initiative (GRI).

Fraud And Greenwashing Risk Management: ISSA 5000 includes provisions to address risks of fraud, greenwashing, and non-compliance with laws and regulations.

Support For Decision-Making: Reliable and assured sustainability information enhancing decision-making for investors, regulators, and other stakeholders.

Existing Assurance Standards And Retirement Dates
There are existing assurance standards that have provided guidelines for engagements other than audits, namely the International Standards on Assurance Engagements (ISAE) 3000 (Revised) and 3410.

ISAE 3000 (Revised) serves as a broad framework for assurance engagements other than audits or reviews of historical financial information, including some sustainability-related engagements. With the introduction of ISSA 5000, ISAE 3000 (Revised) will continue to apply to non-sustainability-related subject matters. Meanwhile, ISAE 3410, which currently addresses assurance engagements on greenhouse gas statements, will be retired on ISSA 5000’s effective date—December 15, 2026. Naturally, the IAASB is encouraging voluntary adoption of ISSA 5000 well ahead of its official implementation date.

Limited vs. Reasonable Assurance
A critical aspect of ISSA 5000 is its distinction between limited and reasonable assurance engagements. Limited assurance provides moderate confidence in reported sustainability information, involving less extensive procedures while still enhancing the reliability of disclosures. In contrast, reasonable assurance offers a higher level of confidence, similar to a financial statement audit, requiring more extensive evidence gathering and verification processes.

The choice between limited and reasonable assurance depends on the complexity of the sustainability information and stakeholder expectations. ISSA 5000 provides clear guidance on applying these assurance levels effectively. That said, it is expected that companies may initially adopt limited assurance before advancing to reasonable assurance as they develop their sustainability reporting maturity and manage costs along their sustainability reporting journey.

ISSA 5000’s Importance To ISSB IFRS S1 & S2
While IFRS S1 & S2 do not mandate assurance, they strongly encourage it, recognising its role in enhancing trust and comparability in sustainability reporting. The ISSB has acknowledged that assurance over sustainability disclosures is critical for investor confidence, and it expects that as regulatory frameworks evolve, more jurisdictions will require assurance over sustainability reporting.

The ISSB standards align with the global push for high-quality, verifiable sustainability information, and the ISSA 5000 provides the assurance framework needed to support this transition. By underpinning assurance engagements for IFRS S1 & S2, ISSA 5000 ensures that businesses and investors can rely on sustainability disclosures that meet global best practices, fostering transparency, accountability, and trust in the evolving sustainability landscape.

The Global Impact Of ISSA 5000
ISSA 5000 and IESSA provide a consistent global approach to sustainability assurance, helping to create a level playing field for all assurance practitioners. These standards were the missing piece in the sustainability reporting jigsaw and support the broader goal of ensuring that sustainability reporting is not only credible but also actionable, driving real progress towards sustainability objectives.

The adoption of ISSA 5000 is expected to play a crucial role in enhancing confidence in sustainability reporting. As sustainability disclosures become more integrated with financial reporting, the need for high-quality assurance will continue to grow, reinforcing the importance of ISSA 5000 in the evolving sustainability reporting landscape.

ISSA 5000 represents a significant milestone in the evolution of sustainability assurance. By providing a robust, globally recognised framework, it ensures that sustainability information is reliable, credible, comparable, and trustworthy— ultimately supporting better decision-making and greater accountability. 

As the demand for sustainability assurance continues to rise, ISSA 5000 will serve as a vital tool for professional accountants and assurance practitioners, helping to shape the future of sustainability reporting worldwide.