The idea of assigning international criminal liability to severe environmental transgressions has made a spectacular comeback in recent years. The overall case for and legal parameters of the crime of ecocide are the subject of heated debates. Considerably less attention has been paid to ways in which ecocide’s criminalization could unravel in practice. What does it take for a prohibitionary norm to gain international legal recognition? In this essay, I draw on legal and empirical literature on the international criminalization process to illustrate the paths that ecocide may take (or could have taken). Such processual knowledge, I argue, is critical to understanding what it may mean for ecocide to become an international crime in the first place.