This article examines the growth of ecological awareness, alongside the emergence of environmental sustainability initiatives, within criminal justice institutions around the world. To date, such developments have received little empirical analysis from criminology scholars. Internationally, this article is among the first to critically analyse the ‘greening’ of policing, courts, prisons, offender supervision and community reintegration. Available literature and examples are reviewed, alongside original research findings. The motivations and ideologies underpinning this nascent green evolution raise deeper questions of ‘why?’ and ‘for whom?’ Innovative examples of sustainable justice architecture and catalysts for penal reform are differentiated from those which claim humanistic intentions and green credentials but, arguably, are based on instrumental fiscal motives that do little to challenge repressive carceral regimes.