This chapter provides an overview of the evolution of “ecocide” as a proposed international crime. It first details how the concept emerged as a response to the use of chemical herbicides in the Vietnam War. It then outlines some of the debates that surrounded the development of an international crime against the environment, debates that ultimately led to the codification of a war crime so watered down as to have barely any real-life applicability. It then explores the rebirth of the campaign to introduce a new crime of ecocide, highlighting several definitions that have been developed in the last few decades. It then interrogates some of the key challenges associated with defining ecocide, as well as the legal and political challenges that might arise if the International Criminal Court is selected as the appropriate forum for this crime.