Genocide is "the deliberate and systematic destruction, in whole or in part, of an ethnic, racial, religious, or national group", though what constitutes enough of a "part" to qualify as genocide has been subject to much debate by legal scholars. While a precise definition varies among genocide scholars, a legal definition is found in the 1948 United Nations Convention on the Prevention and Punishment of the Crime of Genocide (CPPCG). Article 2 of this convention defines genocide as "any of the following acts committed with intent to destroy, in whole or in part, a national, ethnical, racial or religious group, as such: killing members of the group; causing serious bodily or mental harm to members of the group; deliberately inflicting on the group conditions of life, calculated to bring about its physical destruction in whole or in part; imposing measures intended to prevent births within the group; forcibly transferring children of the group to another group."

Raphael Lemkin in his masterpiece "Axis Rule in Occupied Europe" (1943) invented the term "genocide,"by combining "genos" (race, people) and "cide" (to kill).

Lemkin defined genocide as follows: "Generally speaking, genocide does not necessarily mean the immediate destruction of a nation, except when accomplished by mass killings of all members of a nation. It is intended rather to signify a coordinated plan of different actions aiming at the destruction of essential foundations of the life of national groups, with the aim of annihilating the groups themselves. The objectives of such a plan would be the disintegration of the political and social institutions, of culture, language, national feelings, religion, and the economic existence of national groups, and the destruction of the personal security, liberty, health, dignity, and even the lives of the individuals belonging to such groups." The preamble to the CPPCG states that instances of genocide have taken place throughout history, but it was not until Raphael Lemkin coined the term and the prosecution of perpetrators of the Holocaust at the Nuremberg trials that the United Nations agreed to the CPPCG which defined the crime of genocide under international law.

During a video interview with Raphael Lemkin, the interviewer asked him about how he came to be interested in this genocide. He replied; "I became interested in genocide because it happened so many times. First to the Armenians, then after the Armenians, Hitler took action."

There was a gap of more than forty years between the CPPCG coming into force and the first prosecution under the provisions of the treaty. To date all international prosecutions of genocide, the Rwandan Genocide and the Srebrenica Genocide, have been by ad hoc international tribunals. The International Criminal Court came into existence in 2002 and it has the authority to try people from the states that have signed the treaty, but to date it has not tried anyone.

Since the CPPCG came into effect in January 1951 about 80 member states of the United Nations have passed legislation that incorporates the provisions of the CPPCG into their domestic law, and some perpetrators of genocide have been found guilty under such municipal laws, such as Nikola Jorgic, who was found guilty of genocide in Bosnia by a German court (Jorgic v. Germany).

Critics of the CPPCG point to the narrow definition of the groups that are protected under the treaty, particularly the lack of protection for political groups for what has been termed politicide (politicide is included as genocide under some municipal jurisdictions). One of the problems was that until there was a body of case law from prosecutions, the precise definition of what the treaty meant had not been tested in court, for example, what precisely does the term "in part" mean? As more perpetrators are tried under international tribunals and municipal court cases, a body of legal arguments and legal interpretations are helping to address these issues.

The exclusion of political groups and politically motivated violence from the international definition of genocide is particularly controversial. The reason for this exclusion is because a number of UN member nations insisted on it when the Genocide Convention was being drafted in 1948. They argued that political groups are too vaguely defined, as well as temporary and unstable. They further held that international law should not seek to regulate or limit political conflicts, since that would give the UN too much power to interfere in the internal affairs of sovereign nations. In the years since then, critics have argued that the exclusion of political groups from the definition, as well as the lack of a specific reference to the destruction of a social group through the forcible removal of a population, was designed to protect the Soviet Union and the Western Allies from possible accusations of genocide in the wake of World War II.

Another criticism of the CPPCG is that when its provisions have been invoked by the United Nations Security Council, they have only been invoked to punish those who have already committed genocide and have left a paper trail. It was this criticism that led to the adoption of UN Security Council Resolution 1674 by the United Nations Security Council on 28 April 2006 which commits the Council to action to protect civilians in armed conflict and to protect populations from genocide, war crimes, ethnic cleansing and crimes against humanity.

Genocide scholars such as Gregory Stanton have postulated that conditions and acts that often occur before, during, and after genocide—such as dehumanization of victim groups, strong organization of genocidal groups, and denial of genocide by its perpetrators—can be identified and actions taken to stop genocides before they happen. Critics of this approach such as Dirk Moses assert that this is unrealistic and that, for example, "Darfur will end when it suits the great powers that have a stake in the region".

Read more about Genocide:  Criticisms of The CPPCG and Other Definitions of Genocide, Genocide in History, Stages of Genocide, Influences Leading To Genocide, and Efforts To Prevent It, Cultural Genocide