According to the Encyclopædia Britannica Communism (from Latin: communis = "common") is 'a political and economic doctrine that aims to replace private property and a profit-based economy with public ownership and communal control of at least the major means of production (e.g., mines, mills, and factories) and the natural resources of a society. Communism is thus a form of socialism—a higher and more advanced form, according to its advocates. Exactly how communism differs from socialism has long been a matter of debate, but the distinction rests largely on the communists’ adherence to the revolutionary socialism of Karl Marx.'

In political science, the term "communism" is sometimes used to refer to communist states, a form of government in which the state operates under a one-party system and declares allegiance to Marxism-Leninism or a derivative thereof, even if the party does not actually claim that it has already reached communism.

Karl Marx was a revolutionary, sociologist, historian, and economist. He published (with Friedrich Engels) Manifest der Kommunistischen Partei (1848), commonly known as The Communist Manifesto, the most celebrated pamphlet in the history of the socialist movement. He also was the author of the movement’s most important book, Das Kapital. These writings and others by Marx and Engels form the basis of the body of thought and belief known as Marxism.

He helped to form the first openly communist political organizations and firmly tied communism with the idea of revolution conducted by the exploited working class. Marx posited that communism would be the final stage in human society, which would be achieved after an intermediate stage called the revolutionary dictatorship of the proletariat.

The Russian Revolution is the series of revolutions in Russia in 1917, which destroyed the Tsarist autocracy and led to the creation of the Soviet Union. The October Revolution of 1917, led by Vladimir Ilych Ulyanov (also known as Lenin), leader of the Bolshevik Party, was the first large scale attempt to put Marxist ideas about a workers' state into practice.

Leninism refers to various related political and economic theories elaborated by the Bolshevik communist leader Vladimir Lenin. Leninism builds upon and elaborates the ideas of Marxism, and serves as a philosophical basis for the ideology of Soviet communism.

Stalinism is a term coined by Lazar Kaganovich that refers to the political system of the Soviet Union under the leadership of Joseph Stalin, leader of the Soviet Union from 1928–1953. The term implies an inherently oppressive system of extensive government spying, extrajudicial punishment, and political "purging", or elimination of political opponents either by direct killing or through exile, and it involves a state using extensive use of propaganda to establish a personality cult around an absolute dictator to maintain control over the nation's people and to maintain political control for the Communist Party.

Maoism, variably and officially known as Mao Zedong Thought, is a totalitarian variant of Marxism derived from the teachings of the late Chinese leader Mao Zedong, widely applied as the political and military guiding ideology in the Communist Party of China from Mao's ascendancy to its leadership until the inception economic reforms in 1978. It is also applied internationally in contemporary times. Maoist parties and groups exist throughout the world.

Despite its apparent utopian idealism, a distinction must be made between the doctrine of communism and its actual practise. Communism where applied almost univerally imposed wholesale repression , culminating in a state sponsored reign of terror. Communist regimes, in order to consolidate their grip on power turned mass crimes into a full-blown system of government.

According to the The Black Book of Communism: Crimes, Terror, Repression the number of victims killed world-wide is close to 100 million. The breakdown of the number of deaths is as follows:

65 million in the People's Republic of China
20 million in the Soviet Union
2 million in Cambodia
2 million in North Korea
1.7 million in Africa
1.5 million in Afghanistan
1 million in the Communist states of Eastern Europe
1 million in Vietnam
150,000 in Latin America
10,000 deaths resulting from actions of the international communist movement and communist parties not in power.

The Black Book of Communism: Crimes, Terror, Repression is a book which describes a history of repressions, both political and civilian, by Communist states, including extrajudicial executions, deportations, and artificial famines. The book was originally published in 1997 in France under the title, Le Livre noir du communisme : Crimes, terreur, répression. In the United States it is published by Harvard University Press. The book was authored by several European academics and edited by Stéphane Courtois.

The Global Museum on Communism is a project of the non-profit Victims of Communism Memorial Foundation established by an Act of Congress in 1993. The mission of the Museum is to educate this generation and future generations about the history, philosophy and legacy of communism.

The Victims of Communism Memorial Foundation was established by an Act of Congress on December 17, 1993 and signed into law by President Bill Clinton.
Co-sponsored by Representative Dana Rohrabacher, Representative Robert Toricelli, Senator Claiborne Pell and Senator Jesse Helms the legislation authorized the design and construction of The Victims of Communism Memorial in Washington, D.C. for and with the participation of “all groups that have suffered under communism.”

The VOCMF has a three-phase mission:

The 1st phase of the mission, to memorialize the victims of communism, was realized with the dedication of the Victims of Communism Memorial in Washington, DC on June 12, 2007.

The 2nd phase of the mission, to educate the public, has been initiated with the launch of the Global Museum on Communism on June 16th 2009.

The 3rd phase of the mission, to document the evidence, is to be realized with the eventual construction of a permanent self-standing 'bricks and mortar' museum in Washington DC.