This article deals with the elements of definitions of the crime of aggression adopted in February 2009 by an ad hoc Working group. This organ was created by the Assembly of State Parties to the Rome Statute of the International Criminal Court and its conclusions should be examined during the Review Conference of the Rome Statute to be held in spring 2010. In the author’s views, the propositions of the Working group, if ever adopted, would constitute a breach of several international norms and would violate American laws. It would disregard the principle of legality and the United Nations Charter. Politically, the success of the attempt could only face great powers hostility. For instance, if such a definition would have been in force for the last several decades, every US President could have been subjected to prosecution. The same could be said regarding heads of State and military leaders from other places. In sum, it is not reasonable for both ICC credibility and viability to enforce the Working group propositions.