The CPSU was a communist party organized on the basis of democratic centralism, a principle conceived by Lenin that entails democratic and open discussion of policy issues within the party followed by the requirement of total unity in upholding the agreed policies. The highest body within the CPSU was the party Congress, which convened every five years. When the Congress was not in session, the Central Committee was the highest body. Because the Central Committee met twice a year, most day-to-day duties and responsibilities were vested in the Politburo, the Secretariat and the Orgburo (until 1952). The party leader was the head of government and held the office of either General Secretary, Premier or head of state, or some of the three offices concurrently—but never all three at the same time. The party leader was the de facto chairman of the CPSU Politburo and chief executive of the Soviet Union. The tension between the party and the state (Council of Ministers of the Soviet Union) for the shifting focus of power was never formally resolved, but in reality the party dominated and a paramount leader always existed (first Lenin and thereafter the General Secretary).
After the founding of the Soviet Union in 1922, Lenin had introduced a mixed economy, commonly referred to as the New Economic Policy, which allowed for capitalist practices to resume under the Communist Party dictation in order to develop the necessary conditions for socialism to become a practical pursuit in the economically undeveloped country. In 1929, as Joseph Stalin became the leader of the party, Marxism–Leninism, a fusion of the original ideas of Karl Marx and Lenin, became formalized as the party's guiding ideology and would remain so throughout the rest of its existence. The party pursued state socialism, under which all industries were nationalized and a planned economy was implemented. After recovering from the Second World War, reforms were implemented which decentralized economic planning and liberalized Soviet society in general. By 1980, various factors, including the ongoing nuclear arms race with the United States and unaddressed inefficiencies in the economy, led to stagnant economic growth and growing disillusionment. After Mikhail Gorbachev assumed leadership in 1985, rapid steps were taken to transform the economic system in the direction of a market economy once again. Gorbachev and his allies envisioned the introduction of an economy similar to Lenin's New Economic Policy through a program of perestroika, or restructuring, but their reforms along with the institution of free multiparty elections led to a decline in the party's power, and after the dissolution of the Soviet Union, the banning of the party by Boris Yeltsin.
A number of causes contributed to CPSU's loss of control and the dissolution of the Soviet Union. Some historians have written that Gorbachev's policy of glasnost (political openness) was the root cause, noting that it weakened the party's control over society. Gorbachev maintained that perestroika without glasnost was doomed to failure anyway. Others have blamed the economic stagnation and subsequent loss of faith by the general populace in communist ideology. In the final years of the CPSU's existence, the Communist Parties of the federal subjects of Russia were united into the Communist Party of the Russian Soviet Federative Socialist Republic. After the CPSU's demise, the Communist Parties of the Union Republics became independent and underwent various paths of reform. In Russia, the Communist Party of the Russian Federation emerged and has been regarded as the inheritor of the CPSU's legacy into the present day.
The origin of the CPSU was in the Bolshevik faction of the Russian Social Democratic Party, which, under the leadership of Vladimir Lenin, left the party in January 1912 to form a new party at the Prague Party Conference, called the Russian Social Democratic Labour Party (bolsheviks) – or RSDLP(b). Prior to the February Revolution of 1917, the party worked underground as organized anti-Tsarist groups. By the time of the revolution, many of the party's central leaders, including Lenin, were in exile.
With Tsar Nicholas II deposed in February 1917, a republic was established and administered by a provisional government which was largely dominated by the interests of the former nobility. Alongside it, grassroots general assemblies spontaneously formed, which in Russian were called soviets, and a dual-power structure between the soviets and the provisional government was in place until such a time that their differences would be reconciled in a post-provisional government. Lenin was at this time in exile in Switzerland where he, with other dissidents in exile, managed to arrange safe passage back to Russia through the continent amidst the ongoing war. In April, Lenin arrived in Petrograd and condemned the provisional government, calling for the advancement of the revolution towards the transformation of the ongoing war into a war of the working class against capitalism. The revolution did in fact prove to not yet be over, as tensions between the social forces aligned with the soviets and those with the provisional government came into explosive tensions during that summer.