This article focuses on the development of the crime of incitement to genocide and the prohibition of hate propaganda. It first examines the conflict which exists between these and the right to freedom of speech and concludes that a limitation of this right through prohibition of hate propaganda and criminalization of incitement to genocide is justifiable. The article then analyses how the crime of incitement to genocide and the prohibition of hate propaganda first developed historically, focusing on judgments by the International Military Tribunal at Nuremberg and the Genocide Convention, on the one hand, and on international conventions and case law by the Human Rights Committee and the European Court of Human Rights, on the other. Next, recent ICTR decisions are examined, in which the ICTR has considerably clarified and extended the concept of incitement to genocide. The tribunal has brought it closer to encompassing vicious hate propaganda by acknowledging that in order to incite individuals to commit genocide, incitement in the sense of instigation is insufficient; it requires the prior creation of a certain climate in which the commission of such crimes is possible. Hate propaganda leads to the creation of such a climate. It is argued that, for several reasons, virulent hate propaganda must be accorded the status of an international crime. Genocide could be prevented more effectively if such speech were criminalized. Several efforts to outlaw hate propaganda internationally in the past are examined. The article concludes that it can be regarded as a crime punishable under the Genocide Convention if a purposive interpretative approach is used, and that hate propagandists should be prosecuted for direct and public incitement to genocide if their hate speech is engaged in with the specific intent to commit genocide, and creates a substantial danger of genocide.