The Communist Party of Germany (German: Kommunistische Partei Deutschlands, KPD) was a major political party in Germany between 1918 and 1933, and a minor party in West Germany in the postwar period until it was banned in 1956.

Founded in the aftermath of the First World War by socialists opposed to the war, the party became gradually ever more committed to Leninism and later Stalinism after the death of its founding figures. During the Weimar Republic period, the KPD usually polled between 10 and 15 percent of the vote and was represented in the Reichstag and in state parliaments. Under the leadership of Ernst Thälmann from 1925 the party became staunchly Stalinist and loyal to the leadership of the Soviet Union, and from 1928 it was largely controlled and funded by the Comintern in Moscow. Under Thälmann's leadership the party directed most of its attacks against the Social Democratic Party of Germany, which it regarded as its main adversary and referred to as "social fascists"; the KPD considered all other parties in the Weimar Republic to be "fascists."^[8]

The party's paramilitary wing was the Roter Frontkämpferbund ("Alliance of Red Front-Fighters"), which was banned as extremist by the governing social democrats in 1929; in 1932 the KPD also founded Antifaschistische Aktion, commonly known as Antifa, which it described as a "red united front under the leadership of the only anti-fascist party, the KPD," and which largely attacked the "social fascists" [social democrats].^[9] Banned in the Weimar Republic one day after Adolf Hitler emerged triumphant in the German elections in 1933, the KPD maintained an underground organization but suffered heavy losses.

The party was revived in divided postwar West and East Germany and won seats in the first Bundestag (West German Parliament) elections in 1949, but its support collapsed following the establishment of a communist state in the Soviet occupation zone of Germany. The KPD was banned as extremist in West Germany in 1956 by the Constitutional Court. Some of its former members founded an even smaller fringe party, the German Communist Party (DKP), in 1969, which remains legal, and multiple tiny splinter groups claiming to be the successor to the KPD have also subsequently been formed.

In East Germany, the party was merged, by Soviet decree, with remnants of the Social Democratic Party to form the Socialist Unity Party (SED) which ruled East Germany from 1949 until 1989–1990; the forced merger was opposed by the social democrats, many of whom fled to the western zones. After the fall of the Berlin Wall, reformists took over the SED and renamed it the Party of Democratic Socialism; in 2007 the PDS subsequently merged with the SPD splinter faction WASG to form Die Linke.

Before the First World War the Social Democratic Party (SPD) was the largest party in Germany and the world's most successful socialist party. Although still officially claiming to be a Marxist party, by 1914 it had become in practice a reformist party. In 1914 the SPD members of the Reichstag voted in favour of the war. Left-wing members of the party, led by Karl Liebknecht and Rosa Luxemburg, strongly opposed the war, and the SPD soon suffered a split, with the leftists forming the Independent Social Democratic Party of Germany (USPD) and the more radical Spartacist League. In November 1918, revolution broke out across Germany. The leftists, led by Rosa Luxemburg and the Spartacist League, formed the KPD at a founding congress held in Berlin in 30 December 1918 – 1 January 1919 in the reception hall of the City Council^[10] Apart from the Spartacists, another dissent group of Socialists called the International Communists of Germany, also dissenting members of the Social Democratic party, but mainly located in Hamburg, Bremen and Northern Germany, joined the young party.^[11] The Revolutionary Shop Stewards, a network of dissenting socialist trade unionists centered in Berlin were also invited to the Congress, but eventually did not join the party because they deemed the founding congress leaning into a syndicalist direction.

There were seven main reports given at the founding congress:

These reports were given by leading figures of the Spartakus League, however members of the Internationale Kommunisten Deutschlands also took part in the discussions

Under the leadership of Liebknecht and Luxemburg, the KPD was committed to a revolution in Germany, and during 1919 and 1920 attempts to seize control of the government continued. Germany's Social Democratic government, which had come to power after the fall of the Monarchy, was vehemently opposed to the KPD's idea of socialism. With the new regime terrified of a Bolshevik Revolution in Germany, Defense Minister Gustav Noske formed a series of anti-communist paramilitary groups, dubbed "Freikorps", out of demobilized World War I veterans. During the failed Spartacist uprising in Berlin of January 1919, Liebknecht and Luxemburg, who had not initiated the uprising but joined once it had begun, were captured by the Freikorps and murdered. The Party split a few months later into two factions, the KPD and the Communist Workers Party of Germany (KAPD).

Following the assassination of Leo Jogiches, Paul Levi became the KPD leader. Other prominent members included Clara Zetkin, Paul Frölich, Hugo Eberlein, Franz Mehring, August Thalheimer, and Ernst Meyer. Levi led the party away from the policy of immediate revolution, in an effort to win over SPD and USPD voters and trade union officials. These efforts were rewarded when a substantial section of the USPD joined the KPD, making it a mass party for the first time.

Through the 1920s the KPD was racked by internal conflict between more and less radical factions, partly reflecting the power struggles between Zinoviev and Stalin in Moscow. Germany was seen as being of central importance to the struggle for socialism, and the failure of the German revolution was a major setback. Eventually Levi was expelled in 1921 by the Comintern for "indiscipline." Further leadership changes took place in the 1920s. Supporters of the Left or Right Opposition to the Stalin-controlled Comintern leadership were expelled; of these, Heinrich Brandler, August Thalheimer and Paul Frölich set up a splinter Communist Party Opposition.

A new KPD leadership more favorable to the Soviet Union was elected in 1923. This leadership, headed by Ernst Thälmann, abandoned the goal of immediate revolution, and from 1924 onwards contested Reichstag elections, with some success.

During the years of the Weimar Republic, the KPD was the largest communist party in Europe and was seen as the "leading party" of the communist movement outside the Soviet Union.^[12] It maintained a solid electoral performance, usually polling more than 10% of the vote and gaining 100 deputies in the November 1932 elections. In the presidential election of the same year, Thälmann took 13.2% of the vote, compared to Hitler's 30.1%. Under Thälmann's leadership, the party was closely aligned with the Soviet leadership headed by Joseph Stalin, and from 1928 the party was largely controlled and funded by Comintern in Moscow.^[8]

Throughout the Weimar era, the KPD viewed the Social Democratic Party of Germany (SPD) as its main adversary,^[8] and the KPD referred to the SPD as "social fascists."^[13] The KPD regarded itself as "the only anti-fascist party" in Germany and held that all other parties in the Weimar Republic were "fascist".^[8] Nevertheless it cooperated with the Nazis in the early 1930s in attacking the social democrats, and both sought to destroy the liberal democracy of the Weimar Republic.^[14] In the early 1930s the KPD sought to appeal to Nazi voters with nationalist slogans^[8] and in 1931 the KPD had united with the Nazis, whom they then referred to as "working people's comrades," in an unsuccessful attempt to bring down the social democrat state government of Prussia by means of a plebiscite.^[15] While also opposed to the Nazis, the KPD regarded the Nazi Party as a less sophisticated and thus less dangerous fascist party than the SPD, and KPD leader Ernst Thälmann declared that "some Nazi trees must not be allowed to overshadow a forest" of social democrats.^[16]

Critics of the KPD accused it of having pursued a sectarian policy, e.g. the Social Democratic Party criticized the KPD's thesis of "social fascism" (which addressed the SPD as the Communist's main enemy). This scuttled any possibility of a united front with the SPD against the rising power of the National Socialists. These allegations were repudiated by supporters of the KPD as it was said the right-wing leadership of the SPD rejected the proposals of the KPD to unite for the defeat of fascism. The SPD leaders were accused of having countered KPD efforts to form a united front of the working class. For instance, after Papen's government carried out a coup d'état in Prussia the KPD called for a general strike and turned to the SPD leadership for joint struggle, but the SPD leaders again refused to cooperate with the KPD.

Soon after the appointment of Adolf Hitler as Chancellor, the Reichstag was set on fire and Dutch council communist Marinus van der Lubbe was found near the building. The Nazis publicly blamed the fire on communist agitators in general, although in a German court in 1933, it was decided that Van Der Lubbe had acted alone, as he claimed to have done. After the fire, the Reichstag Fire Decree was passed.

Repression began within hours of the fire, when police arrested dozens of Communists. Although Hitler could have formally banned the KPD, he did not do so right away. Not only was he reluctant to chance a violent uprising, but he believed the KPD could siphon off SPD votes and split the left. However, most judges held the KPD responsible for the fire, and took the line that KPD membership was in and of itself a treasonous act. At the March 1933 election, the KPD elected 81 deputies. However, it was an open secret that they would never be allowed to take office; they were all arrested in short order. For all intents and purposes, the KPD was banned as of 6 March, the day after the election.^[17]

The KPD was efficiently suppressed by the Nazis. The most senior KPD leaders were Wilhelm Pieck and Walter Ulbricht, who went into exile in the Soviet Union. The KPD maintained an underground organisation in Germany throughout the Nazi period, but the loss of many core members severely weakened the Party's infrastructure.

A number of senior KPD leaders in exile were caught up in Joseph Stalin's Great Purge of 1937–38 and executed, among them Eberlein, Heinz Neumann, Hermann Remmele, Fritz Schulte and Hermann Schubert, or sent to the gulag, like Margarete Buber-Neumann. Still others, like Gustav von Wangenheim and Erich Mielke, denounced their fellow exiles to the NKVD.^[18] Willi Münzenberg, the KPD's propaganda chief, was murdered in mysterious circumstances in France in 1940. The NKVD is believed to have been responsible.

In East Germany, the Soviet occupation authorities forced the eastern branch of the SPD to merge with the KPD (led by Pieck and Ulbricht) to form the Socialist Unity Party (SED) in April 1946.^[19] Although nominally a union of equals, the SED quickly fell under Communist domination, and most of the more recalcitrant members from the SPD side of the merger were pushed out in short order. By the time of the formal formation of the East German state in 1949, the SED was a full-fledged Communist party, and developed along lines similar to other Soviet-bloc Communist parties.^[20] It was the ruling party in East Germany from its formation in 1949 until 1989. The SPD managed to preserve its independence in Berlin, forcing the SED to form a small branch in West Berlin, the Socialist Unity Party of West Berlin.

The KPD reorganised in the western part of Germany, and received 5.7% of the vote in the first Bundestag election in 1949. But the onset of the Cold War and imposition of an undisguised Communist dictatorship in East Germany soon caused a collapse in the party's support. At the 1953 election the KPD only won 2.2 percent of the total votes and lost all of its seats, never to return. The party was banned in August 1956 by the Federal Constitutional Court of Germany.^[21] The decision was upheld by the European Commission of Human Rights in Communist Party of Germany v. the Federal Republic of Germany. The ban was due to the aggressive and combative methods that the party used as a "Marxist-Leninist party struggle" to achieve their goals.

After the party was declared illegal, many of its members continued to function clandestinely despite increased government surveillance. Part of its membership refounded the party in 1968 as the German Communist Party (DKP). Following German reunification many DKP members joined the new Party of Democratic Socialism, formed out of the remains of the SED. In 1968, a self-named "true successor" to the (banned) West German KPD was formed, the KPD/ML (Marxist–Leninist), which followed Maoist ideas. It went through multiple splits and united with a Trotskyist group in 1986 to form the Unified Socialist Party (VSP), which failed to gain any influence and dissolved in the early 1990s.^[22] However, multiple tiny splinter groups originating in the KPD/ML still exist, several of which claim the name of KPD. Another party with this name was formed in 1990 in East Berlin by several hardline Communists who had been expelled from the PDS, including Erich Honecker. The "KPD (Bolshevik)" split off from the East German KPD in 2005, bringing the total number of (more or less) active KPDs to at least 5.

The Left, formed out of a merger between the PDS and Labour and Social Justice – The Electoral Alternative in 2007, claims to be the historical successor of the KPD (by way of the PDS).

In the early 1920s, the party operated under the principle of democratic centralism, whereby the leading body of the party was the Congress, meeting at least once a year.^[23] Between Congresses, leadership of the party resided in the Central Committee, which was elected at the Congress, of one group of people who had to live where the leadership was resident and formed the Zentrale and others nominated from the districts they represented (but also elected at the Congress) who represented the wider party.^[24] Elected figures were subject to recall by the bodies that elected them.^[25]

The KPD employed around about 200 full-timers during its early years of existence, and as Broue notes "They received the pay of an average skilled worker, and had no privileges, apart from being the first to be arrested, prosecuted and sentenced, and when shooting started, to be the first to fall".^[26]