Sustainability reporting and sustainability assurance are new accounting technologies which have been introduced to assist organisations in transitioning to a sustainable growth model. The overarching research objective guiding this study is to understand how sustainability reporting managers (SRMs) prepare sustainability reports and how sustainability assurance providers (SAPs) undertake sustainability assurance. The study draws on Lawrence and Suddaby’s (2006) typology to understand the forms of institutional work SRMs and SAPs undertake as they perform their roles and how these efforts affect the institutionalisation of sustainability reporting and sustainability assurance. Given the interpretive nature of this research the tenants of hermeneutic theory are used to provide the research methodology and research method to guide the investigation. Data comprises of semi-structured interviews with SRMs and SAPs based in Australia and New Zealand. From the overarching research objective, three research questions are addressed. The first research question explores the supply-side of the sustainability assurance market. The institutional efforts of accounting sustainability assurance (ASAPs) are directed at institutionalising sustainability assurance as similar to or the same as a traditional financial statements audit. In comparison, the institutional efforts of non-accounting sustainability assurance providers (NASAPs) are directed towards institutionalising sustainability assurance as a vehicle designed to drive sustainability within reporting organisations. The second research question explores the institutional work of SRMs as they attempt to institutionalise sustainability reporting within their organisations. SRMs play the role of sustainability reporting champions and sustainability reporting experts. These efforts occur within the backdrop of the new GRI G4 reporting guidelines. As a result, SRMs are changing the normative foundations underlying sustainability reporting from bigger is better to more focused materiality assessment driven reporting. However, while SRMs have been successful in embedding and routinising sustainability reporting these efforts have had a lesser immediate impact in promoting balanced sustainability reporting practices. The third research question focuses on the demand-side of the sustainability assurance market. Given the voluntary nature of sustainability assurance, SAPs institutional efforts are aimed at achieving the dual objectives of enhancing the credibility of sustainability reports and promoting the sustainability assurance as a value added service. However, due to the voluntary nature of sustainability assurance, the efforts of SAPs have had a relatively greater impact in promoting reliable sustainability reporting and less success in promoting balanced sustainability reporting. Finally, the efforts of SAPs in promoting sustainability assurance as a value added activity has also met with difficulties as this study finds that the engagement suffers from diminishing returns. The contributions from this study are both practical and academic. At a practical level, the findings will prove beneficial to inexperienced SRMs. The study recommends that given the voluntary nature of the engagement, there is a need for greater regulation designed to strengthen the position of SAPs. At an academic level, the findings build on the limited body of interpretive research examining the phenomena of sustainability reporting and sustainability assurance. Finally, the findings contribute to the literature on institutional work, building on Lawrence and Suddaby’s (2006) typology of forms of institutional work.