Purpose: This exploratory study investigates the nature and determinants of the internal audit function’s (IAF's) involvement in environmental, social and governance (ESG) assurance and consulting activities. Originality: There is limited understanding and evidence as to why some IAFs are engaged in ESG assurance and/or consulting activities, while others are not, and how the nature and extent of the IAF’s involvement in these issues differ across organisations for those which are involved. Key literature/Theoretical Perspective: The study is informed by extant external ESG assurance and internal audit literature (generally framed within agency and/or institutional theory). Design/Methodology/Approach: A sequential mixed methods approach will be undertaken. Data will be collected through a survey of chief audit executives, followed by interviews to facilitate in-depth investigation of the survey's findings. Research limitations/Implications: The study will provide insights into the nature and extent of the IAF's involvement in ESG assurance and consulting activities. The study is limited to the Australian context. Practical and Social Implications: The findings of the study will be useful to policy makers and external auditors in the process of developing combined assurance models, in examining the level (and determinants of the level) of ESG assurance work done by IAFs, and the extent to which the IAF’s work in these areas can be relied upon in combined assurance models on integrated reporting.