Abstract The protection of the environment is currently of the uppermost importance and all legal fields have to contribute to this goal. This includes criminal law, both on a national and an international level. The debate in international criminal law focusses on a proposal to introduce a new core crime of “ecocide” to the Rome Statute. Much has been contributed to this debate, and often the ultima ratio approach has been mentioned in this context. However, the contents of this principle remain vague. In my article, I assess the ultima ratio principle for international criminal law and apply it to the discussion about the introduction of a new core crime of ecocide to the Rome Statute. My assessment reveals that under the current circumstances, this cannot be considered a good fit. Rather, alternatives exist that are to be expected to serve the urgent interest of protecting the natural environment better.