As the world transitions into an era of mandatory sustainability disclosures, the credibility of reported information has become just as critical as financial reporting itself. With regulators, investors, and businesses increasingly demanding transparency, the International Standard on Sustainability Assurance (ISSA 5000) has emerged as the first truly global benchmark for sustainability assurance. Developed by the International Auditing and Assurance Standards Board (IAASB), it is designed to bring rigour, consistency, and public trust to sustainability disclosures across diverse frameworks and jurisdictions.
In this exclusive conversation with TheCSRUniverse, Mr. Antonis Diolas, Head of Audit and Assurance, ACCA, sheds light on why ACCA and CA ANZ are jointly advocating for consistent adoption of ISSA 5000, how the new standard differs from existing frameworks, and what it means for the future of the accountancy profession. He explains how materiality remains one of the most misunderstood areas in sustainability assurance and shares how ACCA is preparing accountants to become custodians of credible sustainability information.
From tackling the risks of greenwashing to navigating regulatory maturity across markets, Mr. Diolas also discusses the challenges of global harmonisation and the opportunities this standard creates for auditors, businesses, and emerging economies alike. For the next generation of accountants, the message is clear: sustainability assurance is no longer a niche—it is central to shaping a transparent, accountable, and sustainable global economy.
Q&A
Q. What was the primary motivation behind ACCA and CA ANZ jointly advocating for the consistent adoption of ISSA 5000? How does this standard differ from previous sustainability assurance frameworks?
A. The primary motivation behind ACCA and CA ANZ’s joint advocacy for the consistent adoption of ISSA 5000 stems from the accelerating global demand for credible sustainability reporting especially as many jurisdictions move towards mandatory regulatory regimes. In this context, sustainability assurance plays a critical role in reinforcing the credibility and trustworthiness of reported information.
ISSA 5000, developed by the IAASB after extensive global outreach and consultation, is the first truly international sustainability assurance standard. While it is framework-neutral meaning it can be applied regardless of whether a company reports under IFRS Sustainability Disclosure Standards, ESRS, or another framework, it has been designed with the needs of today’s most widely used sustainability frameworks in mind.
Compared to the existing ISAE 3000 (Revised), last updated in 2013, ISSA 5000 provides more specificity and relevant guidance for sustainability assurance in today’s context. While many foundational concepts from ISAE 3000 (Revised) remain embedded, the landscape has evolved significantly, and ISSA 5000 responds to new expectations around transparency, materiality, and practitioner responsibilities.
Worth noting that the IAASB has developed its own detailed implementation guidance which we encourage everyone to read, however, in our guide we wanted to take a step further where using a case study we showcase how the requirements with respect to materiality could look like when applied in practice. We do note that similar to all IAASB standards, ISSA 5000 is a principles-based standard and hence many of its requirements are based on the assurance practitioner’s professional judgement, this is another important element of the standard that we tried to communicate.
ISSA 5000 can be applied to provide assurance on sustainability information relating to any topic or aspects of topics from environmental to social and governance-related and can be applied by both professional and non-professional accountants acting as assurance practitioners, provided they meet the relevant ethical and quality management requirements set out in the standard. ISSA 5000 is therefore a profession agnostic standard.
Q. How does ACCA’s emphasis on sustainability assurance fit within its broader strategy to future-proof the accountancy profession over the next decade?
A. Sustainability assurance is a core part of ACCA’s strategy to future-proof the accountancy profession. As global expectations around transparency, ethics, and sustainability continue to rise, accountants are uniquely positioned to bring trust, rigour, and credibility to sustainability information just as they have long done in financial reporting.
ACCA’s approach focuses on equipping professionals with the skills, tools, and ethical foundations needed to meet these evolving demands. Sustainability reporting and assurance are integrated throughout the ACCA Qualification and further supported by specialised programmes such as our Professional Diploma in Sustainability. Through our policy and insights work, we also ensure the profession’s voice is heard in the shaping of global sustainability and assurance standards.
This emphasis aligns directly with ACCA’s broader strategy which recognises the essential role of accountants in building a sustainable future.
Q. The new guide walks through Scope 1, 2 and 3 emissions. Which aspects of materiality assessment do you find most frequently misunderstood by assurance teams—and how does the case study clarify them?
A. One of the misunderstood aspects of materiality in sustainability assurance is the distinction between materiality for reporting purposes and materiality for assurance. Practitioners may assume that the thresholds used by the reporting entity automatically apply to the assurance engagement, however under ISSA 5000 the assurance provider must exercise professional judgement and make an independent, well-justified materiality assessment based on user needs.
Our guide also addresses misconceptions around using only quantitative thresholds. It illustrates how under ISSA 5000 qualitative factors such as reputational risk, regulatory attention, or stakeholder expectations can influence materiality. Using a step-by-step approach, it demonstrates how practitioners could determine or consider materiality for both quantitative and qualitative disclosures respectively, by exercising their professional judgment, assessing aggregation risk and by taking into consideration the applicable sustainability reporting framework requirements.
In short, the case study brings some principles of ISSA 5000 to life, helping assurance teams apply them with greater clarity, structure, and confidence.
Q. ACCA and CA ANZ have a long-standing strategic alliance. How has this collaboration helped shape global sustainability assurance thought leadership? Are there other international bodies ACCA is working with to scale up awareness and adoption?
A. ACCA’s strategic alliance with CA ANZ has been instrumental in shaping global sustainability assurance thought leadership. Together, we’ve developed a number of practical, forward-looking resources, including our recent case study on materiality under ISSA 5000 — to support practitioners as they navigate the evolving sustainability reporting landscape. Our shared global reach and complementary expertise enable us to engage a wide audience of professionals, regulators, and standard-setters.
Beyond this alliance, ACCA works closely with international bodies such as the IAASB, IESBA, IFAC, and Accountancy Europe, as well as numerous national standard-setters and professional organisations. We contribute through consultations, technical working groups, and policy dialogues to help scale awareness and practical adoption of high-quality sustainability assurance standards. Our ongoing focus is on advancing global consistency, strengthening professional confidence, and reinforcing public trust in sustainability reporting.
Q. How might ACCA work with technology providers or ESG data platforms to embed materiality analytics into assurance workflows?
A. Our case study on materiality under ISSA 5000 highlights the growing need for structured, well-documented materiality assessments in sustainability assurance. As technology continues to evolve across the profession, we recognise its potential to support assurance teams — whether through data analysis, workflow integration, or enhanced documentation.
While the guide is firmly grounded in professional judgment and practical application of the standard, we acknowledge that tools and platforms may have a role to play in helping practitioners apply materiality consistently and effectively. We remain open to exploring opportunities with technology providers in the future, provided they align with the principles of professional scepticism, transparency, and quality assurance.
Q. Have you received any early success stories or feedback from practitioners or businesses applying the ISSA 5000 materiality principles using your guide? How is ACCA engaging with businesses and regulators in emerging markets to increase trust in sustainability assurance?
A. We’ve received encouraging early feedback from a wide range of stakeholders — including practitioners, oversight bodies, and standard-setters who see the materiality case study as a timely and practical tool for applying ISSA 5000 principles. Many have highlighted the value of a real-world case study that demonstrates the application of professional judgment. We’ve also received positive comments on how the case study addresses both the IFRS Sustainability Disclosure Standards and the ESRS, reflecting ISSA 5000’s framework-neutral design. Several stakeholders have expressed interest in the forthcoming publications planned as part of this series.
At the same time, ACCA continues to engage actively with businesses, professional bodies, and regulators across emerging markets to build awareness and trust in sustainability assurance. This includes regional outreach, capacity-building workshops, and participation in local consultations. Our goal is to support the consistent, high-quality adoption of sustainability assurance standards globally, ensuring practitioners in all markets, regardless of size or maturity, are equipped to deliver credible, stakeholder-relevant assurance.
Q. What challenges do you anticipate in achieving global harmonization of sustainability assurance standards, especially when different jurisdictions have varied regulatory maturity?
A. Achieving global harmonisation of sustainability assurance standards is a complex but vital objective. A key challenge lies in the differing levels of regulatory maturity across jurisdictions with variations in reporting frameworks, assurance expectations, and infrastructure. Striking the right balance between global consistency and local relevance will be essential.
Capacity building is also critical, particularly in markets where sustainability assurance is still evolving. This includes developing technical expertise and improving access to reliable data and practical guidance. That’s why resources such as the IAASB’s implementation guidance for ISSA 5000 and our recent case study on materiality are so valuable.
ACCA remains committed to supporting global convergence through continued collaboration with international standard-setters, national regulators, and the profession, working to build trust and drive quality in sustainability reporting globally.
Q. Greenwashing continues to be a concern despite increased disclosures. How does ISSA 5000, in your view, act as a deterrent and bring transparency to assurance engagements?
A. Greenwashing remains a significant concern, even as sustainability disclosures become more common. The introduction of robust frameworks like the IFRS Sustainability Disclosure Standards is a critical step forward helping ensure that companies disclose information that is consistent, comparable, and decision-useful. These standards set a clear baseline for what needs to be reported, reducing the space for selective or misleading narratives.
But high-quality disclosures alone are not enough. This is where sustainability assurance and in particular ISSA 5000 plays a vital role by bringing global consistency, transparency, and rigour to the assurance of sustainability information. It requires practitioners to evaluate whether reported information is not only accurate, but also relevant, balanced, and aligned with stakeholder expectations. ISSA 5000 also promotes clear documentation of materiality judgments, the assurance scope, and the rationale behind key decisions, all of which contribute to trust and accountability.
Q. With sustainability reporting becoming mandatory in many countries, what role do you see professional bodies like ACCA playing in capacity building and assurance standardization?
A. As sustainability reporting becomes mandatory across more jurisdictions, professional bodies like ACCA have a critical role to play in both capacity building and supporting the consistent application of assurance standards.
First, we help prepare the profession by equipping practitioners with the knowledge, tools, and ethical guidance needed to deliver high-quality assurance aligned with international standards regardless of geography or regulatory maturity. We do this through our globally recognised ACCA Qualification, which embeds sustainability, ethics, and assurance throughout, and through our Professional Diploma in Sustainability where across four certificates we offer in-depth knowledge of sustainability frameworks and ethics, sustainability strategy and management, sustainability reporting and sustainability assurance. Our broader work also includes technical resources, case studies, aligned with emerging global standards like ISSA 5000.
Second, we serve as a bridge between global standard-setters and local markets, promoting convergence while recognising practical challenges on the ground. By engaging with regulators, businesses, and professional communities worldwide, we help foster a shared understanding of what high-quality sustainability assurance looks like.
Ultimately, our focus is on strengthening public trust in sustainability reporting and ensuring the profession is well-positioned to meet the evolving expectations of stakeholders, investors, and society at large.
Q. Looking five years ahead, what does success look like for ACCA in championing high-quality sustainability assurance worldwide—and what milestones will tell you the profession is on track?
A. Looking five years ahead, success for ACCA would be to see sustainability assurance embedded as a trusted, high-quality element of corporate reporting worldwide, delivered by a confident, well-prepared profession. We aim to see global standards like ISSA 5000 applied consistently, supported by strong ethics, professional judgment, and stakeholder relevance.
Progress will be marked by broader adoption of international sustainability reporting and assurance standards, particularly in emerging markets, increased uptake of specialised training such as our Professional Diploma in Sustainability, and stronger collaboration between professional bodies, regulators, and standard-setters.
Equally important are qualitative outcomes: enhanced investor confidence, reduced greenwashing, and improved accountability for sustainability performance. A vital milestone will also be the development of regulatory frameworks that oversee both professional accountants and non-professional accountants acting as assurance practitioners, reinforcing trust and quality across markets.
Q. What’s your message to the next generation of auditors and accountants about the importance of sustainability assurance?
A. This is a unique opportunity to step into a growing and purpose-driven space, where your role in sustainability assurance will be central to building a more transparent, accountable, and resilient global economy. As the world faces complex challenges including climate risk and social equity, businesses and stakeholders are counting on trusted professionals to bring rigour, independence, and credibility to sustainability information.
The skills you develop today in areas such as ethics, critical thinking, and sustainability reporting will shape how organisations respond to the expectations of investors, regulators, and wider society.
Sustainability assurance is more than a compliance exercise. It’s about protecting public trust, guiding responsible business decisions, and contributing to long-term value creation. It’s a space where your expertise, curiosity, and values can make a meaningful impact in the world we live in.
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