The Polish People's Republic (1952–1989), formerly the Republic of Poland (1947–1952), and also often simply known as Poland, was a country in Central Europe that existed as the predecessor of the modern-day democratic Republic of Poland. With a population of approximately 37.9 million near the end of its existence, it was the second most-populous communist and Eastern Bloc country in Europe. It was also where the Warsaw Pact was founded. The largest city and capital was Warsaw, followed by the industrial city of Łódź and cultural city of Kraków. The country was bordered by the Baltic Sea to the north, the Soviet Union to the east, Czechoslovakia to the south, and East Germany to the west.

The Polish People's Republic was a unitary communist state established in the country after the Red Army's takeover of Polish territory from German occupation in World War II. Communist control was strengthened through electoral fraud in the 1946 Polish people's referendum and the 1947 Polish parliamentary election. The Polish United Workers' Party (PZPR) became the dominant political faction in a one-party state, but the country had more liberal policies than other socialist states due to its strategic location in the Cold War and internal opposition. The state's official name was the "Republic of Poland" (Rzeczpospolita Polska) between 1947 and 1952 in accordance with the temporary Small Constitution of 1947. The name "People's Republic" was introduced and defined by the Constitution of 1952. The Polish People's Republic was dissolved following the Revolutions of 1989 and the 1990 Polish presidential election, but the post-communist Third Polish Republic retained the 1952 constitution, with amendments, until the introduction of the current constitution on 17 October 1997, abolishing the socialist structure entirely and replacing it with a parliamentary system that has remained in place to the present-day.

The Ministry of Public Security (UB) and later the Security Service (SB) were the chief intelligence agencies that acted as the secret police. The official police organization, Milicja Obywatelska (MO), along with its ZOMO squads, conducted mass surveillance and violent suppression of protests. The various crimes committed to maintain the PZPR in power, especially after the Cold War intensified, included the harsh treatment of protesters, arrest of opposition leaders and in extreme cases, executions, with an estimated 22,000 people killed or disappeared from 1947 to 1989. Despite the numerous economic hardships, some achievements were established during this period, such as the continuing industrialization and urbanization. Universal health care was improved following global trends in medical innovation, and the population almost doubled between 1947 and 1989. Poland also maintained a large standing army, known as the Polish People's Army. In addition, units of the Soviet Armed Forces were also stationed in Poland as in all other Warsaw Pact countries.

In the summer of 1944, the Polish Committee of National Liberation was established by Soviet-backed Polish communists to control territory retaken from Nazi Germany. On 1 January 1945 the committee was replaced by the Provisional Government of the Republic of Poland, all the key posts of which were held by members of the communist Polish Workers' Party.

At the Yalta Conference in February 1945, Stalin was able to present his Western allies, Franklin Roosevelt and Winston Churchill, with a fait accompli in Poland. His armed forces were in occupation of the country, and the communists were in control of its administration. The Soviet Union was in the process of reincorporating the lands to the east of the Curzon Line, which it had invaded and occupied between 1939 and 1941.

In compensation, Poland was granted German-populated territories in Pomerania, Silesia, and Brandenburg east of the Oder–Neisse line, including the southern half of East Prussia. As a result of these actions, Poland lost 77,035 km² (29,743 sq mi) of land compared to its pre-WWII territory. These were confirmed, pending a final peace conference with Germany, at the Tripartite Conference of Berlin, otherwise known as the Potsdam Conference in August 1945 after the end of the war in Europe. The Potsdam Agreement also sanctioned the transfer of the German population out of the acquired territories. Stalin was determined that Poland's new communist government would become his tool towards making Poland a satellite state like other countries in Central and Eastern Europe. He had severed relations with the Polish government-in-exile in London in 1943, but to appease Roosevelt and Churchill he agreed at Yalta that a coalition government would be formed. The Provisional Government of National Unity was established in June 1946 with the communists holding a majority of key posts, and with Soviet support they soon gained almost total control of the country.

In June 1946, the "Three Times Yes" referendum was held on a number of issues—abolition of the Senate of Poland, land reform, and making the Oder–Neisse line Poland's western border. The communist-controlled Interior Ministry issued results showing that all three questions passed overwhelmingly. Years later, however, evidence was uncovered showing that the referendum had been tainted by large-scale fraud, and only the third question actually passed. Władysław Gomułka then took advantage of a split in the Polish Socialist Party. One faction, which included Prime Minister Edward Osóbka-Morawski, wanted to join forces with the Peasant Party and form a united front against the communists. Another faction, led by Józef Cyrankiewicz, argued that the socialists should support the communists in carrying through a socialist program while opposing the imposition of one-party rule. Pre-war political hostilities continued to influence events, and Stanisław Mikołajczyk would not agree to form a united front with the socialists. The communists played on these divisions by dismissing Osóbka-Morawski and making Cyrankiewicz Prime Minister.

Between the referendum and the January 1947 general elections, the opposition was subjected to persecution. Only the candidates of the pro-government "Democratic Bloc" (the PPR, Cyrankiewicz' faction of the PPS, and the Democratic Party) were allowed to campaign completely unmolested. Meanwhile, several opposition candidates were prevented from campaigning at all. Mikołajczyk's Polish People's Party (PSL) in particular suffered persecution; it had opposed the abolition of the Senate as a test of strength against the government. Although it supported the other two questions, the Communist-dominated government branded the PSL "traitors". This massive oppression was overseen by Gomułka and the provisional president, Bolesław Bierut.