This chapter examines the provisions of international criminal law applicable to serious environmental harm, particularly during non-international armed conflicts ('NIAC'). After describing incidents of serious environmental harm arising in armed conflicts, the analysis surveys the provisions of international criminal law applicable to environmental harm during NIACs, including war crimes, crimes against humanity, genocide, and aggression. It then examines the basis for extending to NIACs the protection against military attacks causing excessive environmental harm (set out in Art. 8(2)(b)(iv) of the Rome Statute), which is currently only applicable in IACs. The examination of this possible amendment of the Rome Statute covers a broad range of instruments and laws forming part of international and national legal codes, all addressing grave environmental harm. Finally, the analysis turns to accountability for environmental harm as a facet of jus post bellum, emphasizing the interconnected nature of environmental harm and cycles of violence and atrocities.