Democratic centralism is a Leninist organisational principle of most communist parties, in which decisions are made by a process of vigorous and open debate amongst party membership, and action is subsequently binding upon all members of the party.

Democratic centralism has historically been associated with not only Marxist–Leninist but also Trotskyist parties, and has also occasionally been practised by social democratic and democratic socialist parties, such as South Africa's African National Congress.

Scholars dispute whether and to what extent democratic centralism was implemented in practice in places where they were nominally in force, such as the Soviet Union and the People's Republic of China, pointing to violent power struggles, backhanded political maneuvering, historical antagonisms and the politics of personal prestige. Various socialist states have made democratic centralism the organisational principle of the state in their statutes, with the political power principle being unitary power.

Democratic centralism is a form of organisation that party members are supposed to abide by, both after having seized the government, but also while trying to seize it. Most communist parties have a democratic centralist structure.

In party meetings, a motion (new policy or amendment, goal, plan or any other kind of political question) is moved (proposed). After a period of debate, a vote is taken. If one vote clearly wins (gaining a share of 60% or above among two options, for example) all party members are expected to follow that decision, and not continue debating it. The goal is to avoid decisions being undermined by participants whose views are in the minority. In the development of socialism in the Soviet Union and China, it was implemented in response to rapid political developments, which required faster mechanisms of decision-making.

Before an issue has been voted on and carried out, discussion and criticism is permitted in all forms. Once a resolution is being carried out, discussion and criticism which may disrupt unity in performing the action is forbidden, to ensure that the action is not derailed. In several socialist states, related practices were also adopted to ensure freedom of discussion, such as Mao's "Don't Blame the Speaker".

Some Trotskyist and orthodox Marxist perspectives describe "deficient" forms of democratic centralism as "bureaucratic centralism," often those espoused by Marxist–Leninists. According to these Trotskyists, bureaucratic centralism de-prioritises democracy, and thus fails to serve the interests of the proletariat.

Vladimir Lenin's text What Is to Be Done? from 1902 is popularly seen as the founding text of democratic centralism. At this time, democratic centralism was generally viewed as a set of principles for the organizing of a revolutionary workers' party. However, Vladimir Lenin's model for such a party, which he repeatedly discussed as being "democratic centralist", was the still extant German Social Democratic Party, inspired by remarks made by the social democrat Jean Baptista von Schweitzer. Lenin described democratic centralism as consisting of "freedom of discussion, unity of action".