Metrics do not merely describe an external or objective reality but instead reflect and animate political struggles over what and how to govern. Examples include: Green House Gas inventories, the Extended Continental Shelf, and excess deaths attributable to COVID-19. Applied to environment, the desire to govern is at least as old as modernity, perhaps because we have never been able to fully realize the modern ideal of the dichotomous separation of nature-culture (Latour, 1993). We understand governing – and thus environmental governance – in the Foucauldian sense, i.e. the ensemble of ‘institutions, procedures, analyses and reflections, calculations and tactics that allow the exercise of a specific, albeit complex, form of power over a target population’ (Foucault, 2004, p. 111). In the twenty-first century, environmental governance is far more complex and polycentric than ever before. Another reason for the complexity of the ensemble of environmental governance is that it is effectively an agencement (Callon et al., 2013), composed of human and non-human actors who become the hybrid objects, subjects and authorities involved in the governing of relations that are sometimes incoherent and contradictory. In this special issue, we are concerned in particular with the problems posed by unsustainable interactions among the living and non-living elements of environments, which become the targets of varied forms of ‘ecogovernmentality’ (Luke, 1995). Fundamental to the forms of governmentality employed in the late 20th and early 21st centuries are efforts to both know the environment and its problems in order to manage them, but also the complex interactions between forms of knowing and ways of intervening and managing. STS scholars argue that data – i.e. temporally and/or spatially bounded representations of phenomena – is increasingly seen to be essential for managing environmental systems, practices and politics (Gabrys, 2016). This special issue pushes this argument further by focusing on the eventful lives of metrics that are used to bind knowing and managing into governing instruments (Lascoumes and Le Gales, 2007). Overall, the articles here discuss these questions: In representing environmental realities, how do metrics value some realities over others? How does such knowledge affect trust in the actors who govern the environment? How does such knowledge structure their accountability?