Communist state is a term used by many political scientists to describe a form of government in which the state operates under a one-party system and declares allegiance to Marxism-Leninism or a derivative thereof.

Communist states may have several legal political parties, but the Communist Party is constitutionally guaranteed a dominant role in government. Consequently, the institutions of the state and of the Communist Party become intimately entwined.

What separates Communist states from other one-party systems is the fact that ruling authorities in a Communist state refer to Marxism-Leninism as their guiding ideology. For Marxist-Leninists, the state and the Communist Party claim to act in accordance with the wishes of the industrial working class; for Maoists, the state and party claim to act in accordance to the peasantry. Both systems claim to have implemented a democratic dictatorship of the proletariat, and both claim to be moving towards the gradual abolition of the state and the implementation of communism. These claims have been strongly disputed by opponents of the historical Communist states, including communists who do not subscribe to Marxism-Leninism or who regard these states as bastardizations of the ideology.

Countries where institutions of the communist party and state are intertwined:
People's Republic of China (since 1949); Communist Party of China

Republic of Cuba (Cuban Revolution in 1959, socialist state declared in 1961); Communist Party of Cuba

Democratic People's Republic of Korea (since 1948); Korean Workers' Party officially describes itself as a socialist republic governed according to the ideology of Juche, which is derived from Marxist-Leninist theory.

Lao People's Democratic Republic (since 1975); Lao People's Revolutionary Party

Socialist Republic of Vietnam (since 1976); Communist Party of Vietnam (ruled the Democratic Republic of Vietnam since 1954)

Countries with democratically elected communist parties heading the government are:
Cyprus the Progressive Party of Working People won the 2008 presidential election
Moldova the Party of Communists of the Republic of Moldova has governed the country since 2001

The People's Republic of China is transiting toward a market economy. Laos has removed all the references to Marxism-Leninism, communism and socialism in the Constitution in 1991. Vietnam is "in transition toward socialism in the light of Marxism-Leninism" and Cuba is "a socialist state guided by ideas of Marx, Engels and Lenin and in transition to a communist society". While these countries share a similar system of government, they have adopted very different economic policies over the past 15 years.