Although the importance of measuring and reporting the social and environmental impact of organisational action is increasingly well recognised by both organisations and society at large, existing approaches to impact measurement are still far from being universally accepted. In this context, the stakeholder dynamics within the nascent field of impact investing demonstrate the complexity of resolving potentially differing perspectives on key impact measurement issues such as materiality. This paper argues, from an organisational perspective, that such arenas of contestation can be (...) conceptualised in terms of social justice. Specifically, we draw upon Sen’s notions of ‘arrangement and realisation’ to explore the dynamics of contestation across a range of stakeholders concerning materiality judgements to suggest that such ‘arrangements’ may lead to suboptimal impact outcomes as ‘realisations.’ Our analysis of the nature of materiality contestations in impact measurement reveals the conflicts, tensions and paradoxes evident in this field of action. Empirically, we examine data drawn from 19 cases and 33 interviews. The analysis suggests three arenas of contestation around the materiality of impact measurement: the power dynamics between economically powerful investors and objectified investees; the conflicts between materiality norms and standards; and the interactions between all stakeholders with differing motivations towards radical or incremental materiality. Building upon this analysis, we then discuss how arenas of contested materiality may be mediated by drawing upon Sen’s notions of transcending the individual interests of the invested parties for the greater good via processes of contextualisation and case-specificity. (shrink)