Reliable sustainability information requires more than good standards for reporting and assurance. It also depends on the integrity and independence of the people involved. In December 2024 the International Ethics Standards Board for Accountants (IESBA) approved a package of revisions to address exactly that, and released the final pronouncements in early 2025.
The centrepiece is the International Ethics Standards for Sustainability Assurance (including International Independence Standards), known as IESSA, designed to operate alongside the IAASB's ISSA 5000.
A framework open to all assurance providers
Like ISSA 5000, IESSA is profession-agnostic. It can be applied by professional accountants and by other sustainability assurance practitioners, such as engineering or certification firms. The goal is that the independence of an assurance provider does not depend on its professional background.
IESSA sets independence requirements equivalent to those that apply to audits of financial statements, including restrictions on providing certain non-assurance services to assurance clients and rules on financial interests and long association.
Rules for preparers too
The package also revises the IESBA Code for professional accountants in business who prepare sustainability information. Ethical expectations around preparing and presenting information — avoiding misleading presentation, managing pressure and acting with integrity — now explicitly extend to sustainability reporting.
This recognises that 'greenwashing' risk sits with preparers as much as with assurers.
Using the work of external experts
A related standard addresses the use of external experts, which is common in sustainability engagements involving climate science, biodiversity or engineering data. Practitioners must evaluate an expert's competence, capabilities and objectivity before relying on their work, including threats arising from the expert's interests and relationships.
Effective dates and adoption
The standards are effective for assurance on sustainability information reported for periods beginning on or after 15 December 2026, aligning with ISSA 5000. Early adoption is permitted, and adoption ultimately depends on national regulators and professional bodies — the EU, for example, has been considering its own approach to ethics for sustainability assurance under the CSRD.
Conclusion
IESBA's sustainability standards complete the architecture: reporting frameworks define what to disclose, ISSA 5000 defines how to assure it, and IESSA defines the ethical conduct that makes that assurance credible.
