The Karl-Liebknecht-Haus is a building at Kleine Alexanderstraße and Weydingerstraße. It was the first building on the Platz.  Since 2007, the federal office of the party Die Linke is based in the Karl-Liebknecht-Haus. Also in the house are the bookstore Der kleine Buchladen, the Berlin State Association of die Linke, the Linksjugend.Solid and the student association Die Linke.SDS. It is unclear since when the house was named after Karl Liebknecht.
Installation as the KPD headquarters
The building was built in 1912 as a factory and office building for Rudolf Werth, who owned the “Berliner Türschliesser Fabrik”. Initially, his factory was in the building, as were other companies. At that time it was still called the Adler House due to the Eagle being the symbol of his company. In 1926 the house was bought by the Communist Party of Germany (KPD) and became their headquarters from 1926 until Adolf Hitler came to power.
Because the party was still making alterations to the building, the various departments only moved in gradually. The central committee of the KPD used the house from 1927. There was also the editorial office of the KPD newspaper Rote Fahne, a bookstore and a printing house. Banners on the building facade with strong political messages where a sign of the tensed climate between workers and the state. More and more often the strong mobilizing power that the party exerted on its members and Berlin workers caused conflicts with the police. Not far from the Karl-Liebknecht-Haus, an extra police unit was installed that were supposed to control the Karl-Liebknecht-Haus and, if necessary, break up crowds by force.
When in 1931 near the Karl-Liebknecht-Haus, in front of the Babylon, two police officers were murdered by members of the party in an alleged act of self-protection by members of the KPD, the building was closed for several days occupied by the police and searched again and again.
Horst-Wessel-Haus: the Karl-Liebknecht-Haus under the swastika
Shortly after the National Socialists came to power, the Karl-Liebknecht-Haus was searched again by the police in February 1933 and finally closed. The National Socialists put the swastika flag on the roof. On March 8, 1933, the SA occupied the house. The house was now named after Horst Wessel, and after a renovation, a memorial hall in memory of the Nazi thug has been added to the entrance. First of all, the "Political Police" use the building, which is where their new department for the fight against Bolshevism was installed. In the months that followed, the SA house served as a “wild concentration camp” in which political opponents were interrogated and abused. From 1937 it was the headquarters of the SA Berlin-Brandenburg.
From 1945 until today
At the end of the Second World War, the building was heavily damaged. The Soviet occupiers then handed over the house to the so-called Fundamit Gesellschaft, which was founded in 1946 by the KPD. The house was rebuilt and one floor was added. Initially right from the funding of the GDR it was used by the SED (Central Unity Party of Germany), later it served as an office and guest house for the Institute for Marxism-Leninism at the Central Committee of the SED.
After the fall of the Berlin Wall, it was initially unclear whether the PDS, as a party that emerged from the SED, could retain ownership of the Karl-Liebknecht-Haus. After several legal disputes, house searches of party members and squatting by the party, the building finally became the property of the PDS party, which had its party headquarters there from 1990 to 2007. Since 2007 the federal office of the party Die Linke has been in the Karl-Liebknecht-Haus.
Dr. Ronald Friedmann offered regular tours through the house until 2020. He gave an insight into the non-happening Festival of the Left in the same year via video tour. 
- R. Friedmann: "Die Zentrale. Geschichte des Berliner Karl-Liebknecht-Hauses", Karl Dietz Verlag, Berlin 2011.
- Digital guided tour through the history of the Karl-Liebknecht-Haus