The Italian Communist Party was a communist and democratic socialist political party in Italy. It was founded in Livorno as the Communist Party of Italy on 21 January 1921, when it seceded from the Italian Socialist Party (PSI), under the leadership of Amadeo Bordiga, Antonio Gramsci, and Nicola Bombacci. Outlawed during the Italian fascist regime, the party continued to operate underground and played a major role in the Italian resistance movement. The party's peaceful and national road to socialism, or the "Italian Road to Socialism", the realisation of the communist project through democracy, repudiating the use of violence and applying the Constitution of Italy in all its parts, a strategy inaugurated under Palmiro Togliatti but that some date back to Gramsci, would become the leitmotif of the party's history.

Marxism–Leninism is a communist ideology that became the largest faction of the communist movement in the world in the years following the October Revolution. It was the predominant ideology of most communist governments throughout the 20th century. It was developed in Russia by Joseph Stalin and drew on elements of Bolshevism, orthodox Marxism, and Leninism. It was the state ideology of the Soviet Union, Soviet satellite states in the Eastern Bloc, and various countries in the Non-Aligned Movement and Third World during the Cold War, as well as the Communist International after Bolshevization.