This doctoral research aims to unpack sustainability reporting principles, namely the principle of materiality and the principle of completeness proposed by the Global Reporting Initiative (GRI) G4 guidelines (2013). To this end, the researcher engages with sustainability reporting, transparency and accountability literature and undertakes a two-year fieldwork including 54 interviews in total with corporate sustainability reporting managers, subject matter experts and senior management and a variety of external stakeholders and two non-participatory observations. The academic and empirical contexts will be introduced in the first three Chapters. The thesis then adopts the three-paper approach and thus field materials related to the principle of materiality and completeness are fed into two relatively independent papers (Chapter 4 and Chapter 5). The contribution of the first empirical paper (Chapter 4) is to show how corporate materiality matrix as a form of transparency has the potential to enable dialogue between the reporting entity and its stakeholders. The contribution of the second empirical paper (Chapter 5) lies in the argument that an incomplete corporate sustainability report is not necessarily problematic, as such incompleteness has the potential to be complemented by actions on the ground. Subsequently, drawing upon the methodological challenges that arise in undertaking fieldwork and then in writing up the field materials that underpin the first two papers, the researcher in Paper 3 (Chapter 6) reflects upon the imperfections of interpretive field studies and contributes to the methodological literature by emphasising the need for making such reflections. The thesis will be closed by Chapter 7 with discussions about implications for practice and suggestions for future research.