The Socialist Republic of Romania (Romanian: Republica Socialistă România, RSR) was a communist state that existed officially in Romania from 1947 to 1989 (see Revolutions of 1989). From 1947 to 1965, the state was known as the Romanian People's Republic (Republica Populară Romînă, RPR). The country was an Eastern Bloc state and a member of the Warsaw Pact with a dominant role for the Romanian Communist Party enshrined in its constitutions. Geographically, RSR was bordered by the Black Sea to the east, the Soviet Union (via the Ukrainian and Moldavian SSRs) to the north and east, Hungary and Yugoslavia (via SR Serbia) to the west, and Bulgaria to the south.

As World War II ended, Romania, a former Axis member which had overthrown their pro-Axis government, was occupied by the Soviet Union as the sole representative of the Allies. On 6 March 1945, after mass demonstrations by communist sympathizers and political pressure from the Soviet representative of the Allied Control Commission, a new pro-Soviet government that included members of the previously outlawed Romanian Workers' Party was installed. Gradually, more members of the Workers' Party and communist-aligned parties gained control of the administration and pre-war political leaders were steadily eliminated from political life. In December 1947, King Michael I was forced to abdicate and the People's Republic of Romania was declared.

At first, Romania's scarce post-war resources were drained by the "SovRoms," new tax-exempt Soviet-Romanian companies that allowed the Soviet Union to control Romania's major sources of income. Another drain was the war reparations paid to the Soviet Union. However, during the 1950s, Romania's communist government began to assert more independence, leading to, for example, the withdrawal of all Soviet troops from Romania by 1958. Overall, from the 1950s to the 1970s, the country exhibited high rates of economic growth and significant improvements in infant mortality, life expectancy, literacy, urbanization, and women's rights, but then stagnated in the 1980s.

In the 1960s and 1970s, Nicolae Ceaușescu became General Secretary of the Communist Party (1965), Chairman of the State Council (1967), and the newly established role of President in 1974. Ceaușescu's denunciation of the 1968 Soviet invasion of Czechoslovakia and a brief relaxation in internal repression led to a positive image both at home and in the West. However, rapid economic growth fueled in part by foreign credits gradually gave way to an austerity and political repression that led to the violent fall of his totalitarian government in December 1989.

Many people were executed or died in custody during communist Romania's existence, most during the Stalinist era of the 1950s. While judicial executions between 1945 and 1964 numbered 137, deaths in custody are estimated in the tens or hundreds of thousands. Others were arrested for political, economical, or other reasons and suffered imprisonment or torture.^{[citation needed]}

The 1965 Constitution remained in effect after its dissolution and was amended to reflect Romania's transition to democracy. It was replaced by the current constitution on 8 December 1991, after a nationwide referendum abolished the socialist system of government completely and replaced it with a semi-presidential system.

When King Michael, supported by the main political parties, overthrew Ion Antonescu in August 1944, breaking Romania away from the Axis and bringing it over to the Allied side, Michael could do nothing to erase the memory of his country's recent active participation in the German invasion of the Soviet Union. Romanian forces fought under Soviet command, driving through Northern Transylvania into Hungary proper, and on into Czechoslovakia and Austria. However, the Soviets treated Romania as a conquered territory, and Soviet troops continued to occupy the country on the basis of the Romanians having been active Nazi allies with a fascist government until very recently.

The Yalta Conference had granted the Soviet Union a predominant interest in Romania. The Paris Peace Treaties did not acknowledge Romania as an allied co-belligerent, as the Romanian army had fought hard against the Soviets for the better part of the war, changing sides only when the tides started to turn. The Communists, as all political parties, played only a minor role in King Michael's first wartime government, headed by General Constantin Sănătescu, though their presence increased in the one led by Nicolae Rădescu. This changed in March 1945, when Dr. Petru Groza of the Ploughmen's Front, a party closely associated with the Communists, became prime minister. His government was broad-based on paper, including members of most major prewar parties except the fascist Iron Guard. However, the Communists held the key ministries, and most of the ministers nominally representing non-Communist parties were, like Groza himself, fellow travelers.