"Crime of all crimes" or genocide is considered as such because of the actions which involve the destruction of the human community only because they are other religious, ethnic, racial, or national groups. Although the crime of genocide dates back to the very beginning of man's existence, the real understanding of this act as a crime begins after the Second World War, and the most illustrative example of genocide from that time is the Holocaust. The term genocide was first introduced by Raphael Lemkin, and its legal definition, which is still valid today, was adopted in the Convention on the Prevention and Punishment of the Punishment of Genocide. This paper will deal with the term of genocide throughout its history and genocide as a crime against values protected by international law. This will be followed by explanations on the denial of genocide and the rest of the work will follow the cases that have been or are being conducted on the International Tribunals for Genocide. Due to the overlap between the term of ethnic cleansing and genocide, part of this paper also deals with distinguishing their essential differences. Finally, states have realized that the essence of genocide is inhuman action and that its core stems from the concept of unjustified hatred of the human mind, and therefore those same states take responsibility for such acts. Taking responsibility is best illustrated by the signing of the aforementioned Convention on the Prevention and Punishment of the Crime of Genocide.