The transnational scope of corporate activities often results in extraterritorial environmental harm elsewhere on the planet. Within the European context, two legal developments are challenging this state of affairs. First, several legislative initiatives seek to establish due diligence standards for corporate activities along global supply chains. Second, domestic courts increasingly assume jurisdiction over environmental damage arising from corporations’ subsidiary operations abroad. This article argues that both these developments are emblematic of the transnationalization and judicialization of environmental governance in the twenty-first century. Rather than providing particularized relief only, national judges may become crucial allies in the construction and enforcement of polycentric regimes. However, the advent of unilateral judicial interventions in the environmental affairs of other countries also raises concerns over the international and institutional legitimacy of the emerging corporate accountability apparatus.