Purpose: Despite the increasing recognition that organizations should report on relevant sustainability matters, the importance and value to stakeholders of these reports being independently assured are not well appreciated. The objective of the paper is to underline that such assurance can be (and is) provided by the internal audit function and, in doing so, that function makes a significant contribution to effective corporate governance. Design/methodology/approach: Theoretical in nature, the paper makes reference to a few "real-world" illustrations. It is review in character and in a relatively systematic manner reviews key internal auditing professional standards-guidance in conjunction with prior theoretical and empirical research. Findings: The paper reinforces the argument that reporting of sustainability policies, practices and measures, without independent assurance, is of reduced value to stakeholders. The paper provides evidence to show how, despite the potential to do so, internal auditing has not always been promoted globally in this role. Research limitations/implications: The paper is limited to a theoretical consideration. There is potential for it to be enhanced by further empirical research demonstrating the value of independent internal auditing within sustainability programs and reporting. Originality/value: The paper is possibly the first to make explicit the linkage between the reporting of sustainability and the assurance of such reports. It should help make boards of organizations in emerging markets more aware of internal audit in relation to sustainability in terms of corporate responsibility and governance. © Emerald Group Publishing Limited.