This research focuses on the concept of participation to the commission of a crime by way of omission. It submits that whereas it is established that certain omissions are settled in international law and could trigger the individual criminal responsibility of the accused, for instance under the principle of command responsibility and inaction under duty to act, no other principle of international law could justify the criminalization of any other omission as it was held in the Rutaganira case.The Rutaganira Judgement which is the appendix to this work has been reprinted in this book.